Glossary of Pump Terms (Globalpumps.com.au)

Info: Approx. 680 English pump terms with definitions.
Source: https://www.globalpumps.com.au/glossary-of-pump-terms (retrieved 2021-03-03)

A

Absolute pressure: The absolute pressure is the sum of the gauge or dial pressure and the atmospheric pressure (14.7psi). If your pump gauge reads 150 psi, then the absolute pressure will be 164.7 psi.
Absorbed Power: This is the sum of the hydraulic power (work done by achieving the flowrate and head) and the frictional losses.
Acceleration: The rate of change of velocity. As velocity is measured in distance per unit time (e.g. m/s), acceleration is measured in change in velocity per unit of time (e.g. m/s²).
Accelerometer: A device that measures proper acceleration. Not necessarily the rate of change of velocity, but the weight experienced by a mass at rest in the frame of reference of the device. An accelerometer at rest on the surface of the earth would measure an acceleration of 9.8 m/s² normal to the surface due to gravity.
Accumulator: A device used to prevent the pump cycling on and off each time a tap is opened in a system. It acts to stabilize the pressure by providing excess water storage in conjunction with a flexible bladder that is air pressurized. As water flows out of the system, it is first pulled from the accumulator tank, and as this tank empties, the pressurized bladder expands to prevent the entire system from a pressure drop. Once the tank is empty, the pressure of the system drops, the pump switches on and refills the tank.
Acoustic: Anything pertaining to sound or to waves generated by sound.
Acoustic resonance: Can occur in any closed or open pipe system due to pump excitation pulsation frequency. This happens when the return of the reflected pressure wave coincides with the generation of the next pulse of pressure. In this case a standing wave is formed inside the fluid filled chamber. This can cause catastrophic failure of systems.
Active metal: Prior to passivation, the formation of a thin oxide on the surface of metals to protect them from corrosion, the metal is known as “active”.
Adapter: A coupling that connects the pump to the rest of the system. Allows the pump to integrate with the downstream parts of the system.
Affinity laws: They are a set of laws that relate the variables of performance, (impeller shaft speed, head, flow rate) to power. They are useful to compare the performance of different pumps.
A-gap: The gap between the tips of the blades on an impeller and the inner diameter of the case bore. If the A-gap is too small, this can be a factor in high pump vibration whereas, if the A-gap is too large, recirculation may occur, leading to pump inefficiency.
Air ingestion: Air leaks into the pump, causing cavitation and pump performance degradation. Air ingestion can be due to leaking flanges, valves located above the fluid line, porous intake lines, faulty shaft seals among others.
Alignment: In the pump world, alignment refers to the alignment of the centerline of the pump shaft with the centerline of the driver shaft. This is critical, because a small amount of misalignment on the power end, results in a large amount at the wet end, where the seals are usually located.
Allowable Pipe Stress: This is a measure of the allowable stresses in pipe walls according to ASTM specification A-53, and A-106 among others. The allowable pipe stress is given by the code for a given pipe construction material, and temperature. From these factors, one can calculate the allowable pressure permitted by code.
Alpha sintered: One form of Silicon Carbide. To bond SiC powder into ceramics, the powder is sintered. At temperatures above 1700°C, the alpha form of SiC is formed.
Ambient heat/pressure: The environmental conditions found where the equipment is operating. In this case either the temperature (ambient heat) or pressure (ambient pressure).
Angular contact ball bearing: These ball bearings have races that are displaced with respect to each other along the bearing axis. This allows the bearing to accommodate both radial and axial loads.
Annealing: To make metal stronger through a heating process. The metal is heated to somewhat below its melting temperature.
Anodize: A treatment used in particular on aluminum. The treatment adds a heavy layer of protective oxide coating.
A.N.S.I. Standard: Founded in 1918, the American National Standards Institute is a non-profit organization that oversees the application of voluntary standards for products. These standards apply to pumps manufactured in the United States.
Anti-friction bearing: A ball or roller bearing that reduces friction. Major consideration during maintenance.
Anti-rotation device:A device that prevents one rotating piece from rotating with respect to a second adjacent part. Usually designed as a pin or key.
Anti Vortex Plate: An anti vortex plate does just what it says. It prevents the formation of a vortex at intake suction points by increasing the path length. Vortexes can cause disturbances at vertical intakes by allowing air to enter the system along with the fluid being pumped.
A.P.I. gland: A seal gland that incorporates important safety features as specified by the American Petroleum institute. The main component is a Disaster bushing that prevents sparking of metal components in the event of a bearing failure. Other components include a drain and vent connection and a flushing connection.
API Plan 11: A specification from the American Petroleum Institute used in single seal or in the primary seal of unpressurized dual seals. The purpose of a mechanical seal flushing is to lubricate and cool a pump’s mechanical seal. Plan 11 refers to the specifications to be used in a pump whose impeller has back wear rings.
API Plan 13: A specification from the American Petroleum Institute used in single seal or in the primary seal of unpressurized dual seals. The purpose of a mechanical seal flushing is to lubricate and cool a pump’s mechanical seal. Plan 13 refers to the specifications to be used in a pump whose impeller has NO back wear rings.
API pump: The American Petroleum Institute has published a set of standards (see API 610 to ensure pumps meet minimum safety, reliability and maintainability standards. A pump that conforms to these standards is said to be an “API pump”.
A.P.I. Specifications: Specifications recommended by the American Petroleum Institute. These specify many safety features of pumps and piping involved in pumping flammable or dangerous substances.
API 610: A standard for pumps used in the petrochemical industry published by the American Petroleum Institutute. API 610 ensures that safe, reliable pumps are used in a dangerous industry.
Application: The set of conditions that describe the pumping operation. The description of the process of the particular pumping function. Includes the fluid and the operating conditions.
ASME: American Society of Mechanical Engineers. Society that promotes the “art, science and practice of multidisciplinary engineering and allied sciences around the globe”.
Atmospheric pressure: The pressure that the atmosphere exerts. Measured as the weight of a column of air of a certain cross section. At sea level, the recognized value is 14.7 pounds per square inch (1.03 Kg per square cm).
AVS Standard: An old, obsolete standard that has been replaced by the A.N.S.I.standard. The American Voluntary Standard (AVS), was first proposed in the 1950s.
Axial flow pump: A common pump type that is essentially an impeller in a pipe. The impeller is driven by an electric motor or petrol/diesel engine. The propeller’s rotation causes the fluid to be pumped axially along the pipe.The main advantage of this type of pump is that it has a comparatively high discharge at a low head.
Axial split casing: A casing for a pump that is manufactured in two halves and joined. The join runs along the axis of the pump.
Axial split pump: A pump (usually horizontal) containing an axially split casing.
Axial Thrust: The forces acting along the axis, usually generated by the pump impeller.
Axial Thrust Balancing: The principles of axial thrust are easy to understand, an impeller wants to move in an axial direction with a lot of force. As it cannot, the fluid moves instead. To help balance this thrust, a method (balancing drum or balancing disk or both) is employed.
Absolute pressure: The absolute pressure is the sum of the gauge or dial pressure and the atmospheric pressure (14.7psi). If your pump gauge reads 150 psi, then the absolute pressure will be 164.7 psi.
Absorbed Power: This is the sum of the hydraulic power (work done by achieving the flowrate and head) and the frictional losses.
Acceleration: The rate of change of velocity. As velocity is measured in distance per unit time (e.g. m/s), acceleration is measured in change in velocity per unit of time (e.g. m/s²).
Accelerometer: A device that measures proper acceleration. Not necessarily the rate of change of velocity, but the weight experienced by a mass at rest in the frame of reference of the device. An accelerometer at rest on the surface of the earth would measure an acceleration of 9.8 m/s² normal to the surface due to gravity.
Accumulator: A device used to prevent the pump cycling on and off each time a tap is opened in a system. It acts to stabilize the pressure by providing excess water storage in conjunction with a flexible bladder that is air pressurized. As water flows out of the system, it is first pulled from the accumulator tank, and as this tank empties, the pressurized bladder expands to prevent the entire system from a pressure drop. Once the tank is empty, the pressure of the system drops, the pump switches on and refills the tank.
Acoustic: Anything pertaining to sound or to waves generated by sound.
Acoustic resonance: Can occur in any closed or open pipe system due to pump excitation pulsation frequency. This happens when the return of the reflected pressure wave coincides with the generation of the next pulse of pressure. In this case a standing wave is formed inside the fluid filled chamber. This can cause catastrophic failure of systems.
Active metal: Prior to passivation, the formation of a thin oxide on the surface of metals to protect them from corrosion, the metal is known as “active”.
Adapter: A coupling that connects the pump to the rest of the system. Allows the pump to integrate with the downstream parts of the system.
Affinity laws: They are a set of laws that relate the variables of performance, (impeller shaft speed, head, flow rate) to power. They are useful to compare the performance of different pumps.
A-gap: The gap between the tips of the blades on an impeller and the inner diameter of the case bore. If the A-gap is too small, this can be a factor in high pump vibration whereas, if the A-gap is too large, recirculation may occur, leading to pump inefficiency.
Air ingestion: Air leaks into the pump, causing cavitation and pump performance degradation. Air ingestion can be due to leaking flanges, valves located above the fluid line, porous intake lines, faulty shaft seals among others.
Alignment: In the pump world, alignment refers to the alignment of the centerline of the pump shaft with the centerline of the driver shaft. This is critical, because a small amount of misalignment on the power end, results in a large amount at the wet end, where the seals are usually located.
Allowable Pipe Stress: This is a measure of the allowable stresses in pipe walls according to ASTM specification A-53, and A-106 among others. The allowable pipe stress is given by the code for a given pipe construction material, and temperature. From these factors, one can calculate the allowable pressure permitted by code.
Alpha sintered: One form of Silicon Carbide. To bond SiC powder into ceramics, the powder is sintered. At temperatures above 1700°C, the alpha form of SiC is formed.
Ambient heat/pressure: The environmental conditions found where the equipment is operating. In this case either the temperature (ambient heat) or pressure (ambient pressure).
Angular contact ball bearing: These ball bearings have races that are displaced with respect to each other along the bearing axis. This allows the bearing to accommodate both radial and axial loads.
Annealing: To make metal stronger through a heating process. The metal is heated to somewhat below its melting temperature.
Anodize: A treatment used in particular on aluminum. The treatment adds a heavy layer of protective oxide coating.
A.N.S.I. Standard: Founded in 1918, the American National Standards Institute is a non-profit organization that oversees the application of voluntary standards for products. These standards apply to pumps manufactured in the United States.
Anti-friction bearing: A ball or roller bearing that reduces friction. Major consideration during maintenance.
Anti-rotation device:A device that prevents one rotating piece from rotating with respect to a second adjacent part. Usually designed as a pin or key.
Anti Vortex Plate: An anti vortex plate does just what it says. It prevents the formation of a vortex at intake suction points by increasing the path length. Vortexes can cause disturbances at vertical intakes by allowing air to enter the system along with the fluid being pumped.
A.P.I. gland: A seal gland that incorporates important safety features as specified by the American Petroleum institute. The main component is a Disaster bushing that prevents sparking of metal components in the event of a bearing failure. Other components include a drain and vent connection and a flushing connection.
API Plan 11: A specification from the American Petroleum Institute used in single seal or in the primary seal of unpressurized dual seals. The purpose of a mechanical seal flushing is to lubricate and cool a pump’s mechanical seal. Plan 11 refers to the specifications to be used in a pump whose impeller has back wear rings.
API Plan 13: A specification from the American Petroleum Institute used in single seal or in the primary seal of unpressurized dual seals. The purpose of a mechanical seal flushing is to lubricate and cool a pump’s mechanical seal. Plan 13 refers to the specifications to be used in a pump whose impeller has NO back wear rings.
API pump: The American Petroleum Institute has published a set of standards (see API 610 to ensure pumps meet minimum safety, reliability and maintainability standards. A pump that conforms to these standards is said to be an “API pump”.
A.P.I. Specifications: Specifications recommended by the American Petroleum Institute. These specify many safety features of pumps and piping involved in pumping flammable or dangerous substances.
API 610: A standard for pumps used in the petrochemical industry published by the American Petroleum Institutute. API 610 ensures that safe, reliable pumps are used in a dangerous industry.
Application: The set of conditions that describe the pumping operation. The description of the process of the particular pumping function. Includes the fluid and the operating conditions.
ASME: American Society of Mechanical Engineers. Society that promotes the “art, science and practice of multidisciplinary engineering and allied sciences around the globe”.
Atmospheric pressure: The pressure that the atmosphere exerts. Measured as the weight of a column of air of a certain cross section. At sea level, the recognized value is 14.7 pounds per square inch (1.03 Kg per square cm).
AVS Standard: An old, obsolete standard that has been replaced by the A.N.S.I. standard. The American Voluntary Standard (AVS), was first proposed in the 1950s.
Axial flow pump: A common pump type that is essentially an impeller in a pipe. The impeller is driven by an electric motor or petrol/diesel engine. The propeller’s rotation causes the fluid to be pumped axially along the pipe.The main advantage of this type of pump is that it has a comparatively high discharge at a low head.
Axial split casing: A casing for a pump that is manufactured in two halves and joined. The join runs along the axis of the pump.
Axial split pump: A pump (usually horizontal) containing an axially split casing.
Axial Thrust: The forces acting along the axis, usually generated by the pump impeller.
Axial Thrust Balancing: The principles of axial thrust are easy to understand, an impeller wants to move in an axial direction with a lot of force. As it cannot, the fluid moves instead. To help balance this thrust, a method (balancing drum or balancing disk or both) is employed.

B

BA: The width of the impeller in a pump. Commonly measured from the OD of the impeller excluding the width of the impeller walls. This measure is proportional to pump capacity.
Back plate: Used in some centrifugal pumps. The back plate consists of a gland ring facing the bearing side where the mechanical seal or gland packings are arranged in such a way that the pumped fluid cannot leak. The other side of the back plate is situated towards the impeller and becomes one of the wall between the suction casing.
Back pull out pump: A pump design that allows the entire power end of the pump to be removed for maintenance/replacement while the wetend of the pump remains in place.
Back-to-back: In the case of impellers, an arrangement where two impellers are placed back to back on a single shaft sharing the same backplate. This arrangement provides almost double the flow of a single impeller design.
Back to back double seal: A mechanical seal configuration typically used when the process fluid is toxic, flammable, or hazardous. This seal is used to prevent the process fluid or its vapour from leaking into the environment.
Back Vane: Part of the design scheme in impellers used to balance axial thrust on an impeller.
"Bad actor" pump: A pump that fails more frequently than it should based on its MTBF (Mean Time Between Failure).This pump is the type of pump that is ripe for replacement or overhaul.
Balance Holes: Another impeller feature that helps to balance axial thrust.
Balance Ratio: The standard balance ratio is 70-30 used by most mechanical seal companies. This means that 70% of the seal face area is exposed to the hydraulic closing force, while 30% is not.
Balanced seal: The most effective tool to counter heat generation in the stuffing box. The area of the seal face is reduced (i.e. balanced) to reduce the heat generation between the two faces of the seal.
Ball bearing: A bearing that uses balls to maintain the separation between the bearing faces.
Ball shuttling: A situation where the balls in a ball bearing rotate perpendicular to their rolling axis. This can result in premature failure of the bearing by accelerating the microscopic wear. This can be seen as an appearance of a polished raceway.
Bar: Non-SI unit of pressure. Exactly equal to 100,000 Pa. About equal to the atmospheric pressure at sea level.
Barometric pressure: Another term for atmospheric pressure. Often used in weather reports.
Barrel pump: A pump used to transfer fluid from a barrel.
Barrier fluid/liquid: The fluid used between the two mechanical seals of a double seal. Used to isolate the process fluid from the atmosphere. Also known as buffer fluid.
Base circle: A reference circle in a volute design that is used as a basis calculating the cutwater diameter. In most cases, the base circle diameter corresponds to the maximum impeller diameter.
Base plate: The plate on which the pump and motor are mounted.
Bayonet: The mechanical seal drive lugs wear into the drive slots and prevent the seal faces from moving forward to compensate for wear.
Bearing: A machine element that one part to support (i.e. bear) another. They constrain relative motion between moving parts to only the desired motion (e.g. rotation around an axis).
Bellows: Part of the design in a mechanical seal that prevents the build up of deposits on dynamic gaskets.
Bellows plate: Metal bellows in mechanical seals contain thin stamped plates welded together to form a convolution. Each of these plates is known as a bellows plate.
Belt Drive: A series of belts and pulleys that transfer the torque from a drive shaft to the required shaft at the correct speed.
B.E.P.: Best Efficiency Point. The kinetic energy that a pump produces is never converted with 100% efficiency to pressure energy. There are always losses due to friction in the seals/bearings, friction of the pumped fluid over the impeller, etc. The BEP is thevolumetric flow rate of the pump for which the pump was designed to convert the most kinetic energy into pressure energy.
Bernoulli's Law: Describes the behavior of fluid under varying conditions of flow and height. Formulated by Daniel Bernoulli in 1738.
B-gap: The radial gap between the impeller vanes and the volute tongue or diffuser vanes. Careful attention to this gap can keep vibrations down.
B.H.P.: Brake horsepower. The measure of an engine’s horsepower before the loss in power caused by any load (gearbox, etc.). Measured by attaching a “De Prony brake” to the engine’s shaft.
Bingham plastic: A material that behaves as a rigid body at low stress, but flows as a viscous fluid at high stress.Mayonnaise and toothpaste are common examples of this type of material.
Body bound bolts: A bolt/bolt hole configuration where there is an interference between the bolt and its mating hole.
Bourdon pressure gauge: The Bourdon tube is a sealed tube that changes shape in response to applied pressure, causing an attached indicator to reflect a pressure change. This is the most common pressure sensing gauge in use.
Bowl (vertical turbine pump): In multi-stage vertical turbine pumps, the bowl is the casing of one of the stages.
Brinnell hardness: A scale for measuring hardness of materials. It uses an indenter to penetrate the material using a certain force, and characterizes the indentation made.
Buffer fluid: The fluid used between the two mechanical seals of a double seal (see barrier fluid).
Buna N: Commonly known as Nitrile rubber. It is a synthetic rubber that is a copolymer between acrylonitrile and butadiene.
Bushing: An independent plain bearing that is inserted into a housing to provide a bearing surface. For use in rotary applications.
Bypass line: A design that bypasses a portion of the pump system. This can be from the discharge to the stuffing box, the stuffing box to the pump suction or the pump discharge to any lower pressure point in the system.

C

C frame adapter: Alignment of the pump shaft with the driver shaft is critical for efficient pumping. The C frame adapter is one method to help accomplish this.
Calculation software: Calculating fluid mechanics solutions manually, to determine pump ratings and sizes as well as piping run lengths, diameters and flow rates can be a tedious process with many points where errors can be introduced. There are several software packages that can resolve complicated systems with many components, and perform all the necessary calculations, allowing the end user to focus on choosing the appropriate pump according to the calculated parameters.
Canned pump: A pump in which the armature, and shaft of the motor are in a can, used for pumping clean lubricating fluids.
Cantilevered pump:Centrifugal pumps often used in sump pump applications where it’s not desirable to have the bearings/motor under water. The impeller is at the end of a shaft which is cantilevered from the bearing housing assembly. Also known as an overhung pump.
Capacity: The amount of liquid pumped per unit time. Measured in gallons/min, cubic meters per sec, etc.
Carbide:A series of compounds formed when carbon combines with an element. Very hard and often used in seals and as cutting tools for metals. For example, Silicon Carbide.
Carbon bushing: A bushing made of carbon. Often used as a thermal barrier in high temperature application. Can also be used as a disaster bushing and to support a deflecting shaft in many mechanical seal applications.
Carbon/graphite: An element commonly used as in mechanical seals as part of the face, as carbon is chemically inert when it comes into contact with most other fluids.
Carbonizing: Production of carbons at seals. Can interfere with proper movement of the seal and cause leakage.
Carcinogen : Any chemical that has the propensity to cause cancer.
Cartridge seal: An assembly containing the seal, gland sleeve and the rotating seal faces. Because it is self contained in can be installed without any measurement. Used in API seals.
Case: The part of the pump that is the volute chamber, encloses the impeller(s). The case can be split radially or axially.
Case crowning: In a horizontal split centrifugal pump this is a method of transferring a higher amount of the bolt load towards the case bore to better seal the case gasket and prevent washout. It’s recommended when working above 2150 psi.
Case retiring thickness: As cases wear, the wall thickness diminishes due to erosion or corrosion. The thickness of the case at which it will be retired is known as the case retiring thickness.
Catalyst: A chemical that is added to a reaction to speed the reaction up. It is not consumed by the reaction.
Cavitate: Formation of cavities (bubbles) in fluid flow applications in areas of low pressure, causing a collapse in the high pressure area of the pump and loss of capacity, excessive noise and possibly damage.
Center line design: A pump design where the pump is attached to feet that are attached to the sides of the volute instead of the bottom. Commonly used in high temperature pumping applications.
Centipoise: A unit of dynamic viscosity. Equivalent to 1 mPa second.
Centistoke: A unit of kinematic viscosity. Also sometimes referred to as diffusivity of momentum. The kinematic viscosity in centistokes is equal to the dynamic viscosity in cP divided by the liquid density.
Centrifugal force: This is the apparent force that causes a rotating body to move away from the centre of rotation. Not to be confused with centripetal force. Caused by inertia of the rotating body as it’s path is continuously redirected.
Centrifugal pump: A pump that transports fluids by conversion of rotational kinetic energy into hydrodynamic energy of fluid flow. Typically fluid enters the pump near to the rotating axis, and is accelerated by an impeller, flowing radially outward to a volute chamber where it exits the pump.
Centrifugalseparator: Uses centripetal force to separate solids from liquids.
Ceramic: In general, ceramics are inorganic, nonmetallic solids. They may be crystalline or amorphous. They are produced by heating followed by subsequent cooling.
Change of state: When a substance changes from one state to another. For example, solid to liquid, liquid to gas, or solid to gas.
Check valve: A mechanical device that allows flow of a liquid in one direction only. A one-way valve that prevents fluid from flowing backwards in a pump.
Chemraz®: An elastomer used to produce seals with high chemical resistance, retaining efficient elastic qualities. Registered trademark by Green, Tweed.
Chloride stress corrosion: Stress corrosion refers to the growth of cracks in a corrosive environment. Certain stainless steels and aluminium alloys are subject to stress corrosion in the presence of chloride.
Chopper pump: A pump in which the impeller also acts as a cutting blade. Used with solid containing fluid applications to prevent pump blockage.
Chromecarbide: Produced when stainless steel is welded. Forms in the heat affected zone when chrome combines with carbon.
Chrome Oxide: The protective layer (passivated layer) that forms on stainless steel to prevent further oxidation.
Circular casing: A type of casing used in centrifugal pumps when the pump is used for circulation rather than building pressure/head.
Clam Shell: Used to set the distance between convolutions during the production of a metal bellows.
Close coupled: The situation when the pump impeller is mounted directly on the rotating drive shaft. There are no separate bearings.
Close-coupled pump: A pump in which the impeller is mounted on the drive shaft. Close-coupled pumps have the advantage of being compact, but are limited in size.
Closed or open impeller: In a closed impeller, the impeller vanes are contained within a shroud, causing the fluid to always be in contact with the impeller. An open impeller lacks this shroud. Closed impellers are more efficient, but can also clog easier if the process fluid contains solids.
Closed impeller: An impeller whose vanes are completely enclosed by two shrouds, one on the front and one on the back.
Coated Face: When the face of a seal is plated or welded onto the base of the seal, made of a softer material.This design can present problems if the two metals in question have different thermal expansion rates.
Coke: A fuel produced by heating or“cracking” petroleum products. It can interfere with seals of pumps.
Colebrook equation: In fluid mechanics, it’s important to understand the friction caused by interaction of the fluid with the internal surface of the pipe. The Colebrook (a.k.a. Colebrook andWhite) equation is one equation that can be used to calculate the friction factor of a fluid flowing in a pipe.
Composite: In the context of mechanical seals, it refers to either a non-metallic material or a combination of a non-metallic face inserted into a metallic base material.
Compression set: Rubber seals become “compression set” when they are overheated. Elastomeric material loses its shape and takes on a new shape. Can cause leaks in seals.
Concentric dual seal: A dual seal where one seal is situated concentrically within another seal. Used when radial dimensions are not limiting.
Concentricity: When rotating parts each share the same axis of rotation, they are said to be concentric with each other.
Condensate: The fluid formed after a vapour has condensed. For example, water is a condensate of steam.
Constant Level Oiler: A means to maintain the correct oil level in a bearing housing. Automatically replenishes oil as it is used.
Convection: Fluid movement caused by local differences in density. Areas of hot fluid (less dense) will naturally rise, while colder fluid (denser) will sink.
Convection tank: A container used to hold the fluid between two mechanical seals. Integrated heater/coolers are used to control the temperature of the barrier fluid.
Convolution : During construction of metal bellows plates, when they are welded together, they form a convolution.
Cooling jacket: An extra casing surrounding the stuffing box to control the temperature of the process fluid within the stuffing box.
Corebox: Metal parts that are cast have an outer“pattern” – the pattern that is found on the outer surface of the casting, and an inner “corebox” – the pattern that is found on the inside of the casting.
Corrosion resistant: Corrosion resistant material must corrode at less than the the following rates: less than 0.002 inches (0.05 mm) per year.
Coupling: A connection between the pump shaft and the motor shaft. Can compensate for axial movement, but not radial misalignment.
Cover: In a radial split pumps, it’s the part of the pump that completes the case.
Critical speed: Objects that are elastic (e.g. Orings) will have natural resonant frequencies. When a pump/shaft rotates at this frequency, minor imbalances will be magnified. The speed where these natural frequencies occur are called critical speeds.
Cryogenic: Very low temperatures.
Cutwater: DA device that directs the process fluid to the pump discharge pipe.
Cutwater diameter: The cutwater diameter is an important measurement in a centrifugal pump. It is used to determine the appropriate B-gap and limit pressure pulsations and forces to reasonable levels.
CV coefficient: The flow coefficient of a mechanical device that is an indicator of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across an opening and the flow rate.
Cyclone separator: A device that separates solids from liquids by using centrifugal force.

D

Damping: Where vibration is occurring, physically touching a vibrating component is the process of damping.
Darcy-Weisbach equation: An equation used for calculating the friction head loss for fluids in pipes, the friction factor f must be known and can be calculated by the Colebrook, theSwamee-Jain equations or the Moody diagram.
DCI: DCI is an acronym that stands for Disassembly, Cleaning and Inspection. This is the first step in any maintenance, repair or upgrade.
Dead ending: A procedure that isolates the stuffing box. There are no flushing lines or recirculation lines coming in or going out.
Dead head: A dead head is a dangerous situation occurring when the pump is running but there is no discharge, either due to blockage in the line, or an inadvertently closed valve. The pump will continue to operate until a safety shutoff pressure is reached. Prior to this, recirculation within the pump may cause overheating and damage to the pump.
Decanting: Gradually pumping from one container to another.
Deflection: Movement of an axially situated shaft in a radial direction. Density: The mass per unit volume of a material. Often measured in g/ml, or g per cubic centimeter.
Design Duty Point: This is the point on a pump’s efficiency graph for which the design has been optimized. It will be expressed as a particular capacity at a head or pressure of the process fluid. Ideally, this point should coincide with the pump’s best efficiency point.
De-staging: In multi-stage pumps with multiple impellers, de-staging refers to the removal of one or more impellers to reduce the head.
D-frame adapter: A device used to align the shaft on the pump to the shaft on the motor. D-frames are used when the system in question is manufactured in metric dimensions, while a C-frame is used with standard dimensions.
D-Gun process: An alternative to the plasma process for metal deposition. Normally used to put hard metal over softer metal.
Dial indicator: An indicator used to test how well a shaft is aligned axially. Any displacement will cause the indicator to deflect.
Diaphragm pump: Also known as a positive displacement pump, or an air-operated diaphragm pump. Diaphragm pumps with double diaphragms have smooth operation. These pumps are exceptional at pumping liquids that are viscous, toxic, chemically aggressive, or abrasive.
Differential Pressure: The differential pressure is the difference between the pressure of the system at the inlet and outlet of the pump.
Diffuser: Set within the discharge region, the diffuser reduces turbulence of the discharged liquid by promoting a gradual decrease in velocity. It’s usually a set of vanes that are an integral part of the pump.
Dilatant: A liquid that behaves in a non-Newtonian fashion in that it increases in viscosity as the shear strain applied increases. As an example, a mixture of cornstarch and water behaves as a dilatant.
Dilatant liquid: A liquid whose viscosity increases with increased shear rate e.g. agitation. A liquid that behaves in a non-Newtonian fashion in that it increases in viscosity as the shear strain applied increases. As an example, a mixture of cornstarch and water behaves as a dilatant.
D.I.N. standard: A standard published by the “Deutsches Institut für Normung” or German Institute for Standardization.
Disaster bushing: Used in A.P.I. glands to support the shaft in the event of a bearing failure, or to prevent product from rushing to atmosphere after a seal failure. The close clearance (0.025 inch or 0.5 mm.) directs most of the leakage through a drain connection in the seal gland to an appropriate container.
Discharge Head: The discharge head is the pressure at the discharge or outlet.
Discharge recirculation: Discharge recirculation is when the recirculation, or flow reversal happens at the discharge tips of the impeller vanes. Connecting a line from the discharge side of the pump to the stuffing box. Should be used with a close fitting bushing in the end of the stuffing box to increase the stuffing box pressure. A common application when pumping a fluid close to its vapor point.
Displacement: The change in position of an object over time usually with reference to its starting position. Can also refer to dynamic movement when it usually refers to peak-to-peak displacement.
DN factor: Do not use precision bearings if the bearing bore (millimeters) x rpm. is 300,000 or greater.
Dosing: A controlled method of pumping in order to discharge exact amounts of fluid.
Double balanced seal: A seal that is hydraulically balanced in both directions. This is a desirable characteristic, but one that is rarely provided by manufacturers.
Double row, deep groove, ball bearing: A ball bearing configuration in which the rows of balls are positioned to allow the load to be transmitted in an outward converging angle, to increase the thrust load capacity.
Double seal: A pump with two mechanical seals on the drive shaft. Designed to prevent the process fluid from leaking. Used when pumping dangerous liquids.
Double suction pump: In this type of pump the process fluid is channeled inside the casing to both sides of the impeller. This is a very stable configuration as the hydraulic forces are balanced.
Double suction impeller: An impeller that has two inlets, where the liquid enters the impeller from both sides. Stable configuration, as the hydraulic forces are balanced, but expensive to implement.
Double volute: A centrifugal pump in which there are two cutwaters to prevent shaft deflection when the pump is not operating at its best efficiency point.
Drawdown: The decrease in volume of a liquid in a container due to a pump’s removal of the liquid. Usually refers to the decrease in liquid height along the container’s walls.
Drive collar: In a cartridge seal, this is the part that connects the seal sleeve to the shaft. It transmits rotation and prevents axial movement of the sleeve.
Drive lugs: A more robust method of transmitting the torque to the seal face, rather than setscrews.
Drooping curve: A pump efficiency curve in which at low flow, the head rises and then drops as it gets to the shut-off head point.
Dry critical speed: This is the definition from API610: "a rotor's natural frequency calculated assuming that the rotor is supported only at its bearings and that the bearings are of infinite stiffness." In layman’s terms this just means that this calculation does not take into account any of the damping affects of the process fluid. See wet critical speed for a comparison.
Dry running: Running without any process fluid when referring to a pump, or without any lubricant for a seal.
Dual Seal: Two seals in one of several possible configurations. They can be back-to-back, face-to-face, tandem or concentric.
Dual mechanical seal: In a dual mechanical seal configuration, there are two seals in the same chamber arranged in one of several possible positions, tandem, concentric, face-to-face, or back-to-back.
Ductility: The ability of a metal to deform without breaking. Often characterized by how easy it is to stretch the material into a wire.
Dynamic Elastomer: The elastic components of the seal that must compensate for seal face wear or shaft movement. Usually made of rubber or other elastic polymer.
Dynamic head (system head): The dynamic head is the component of the total dynamic head caused by friction in the system, due to interaction of the process fluid with the pipe walls.
Dynamic unbalance: A situation where the axis of inertia of a rotor (impeller) is not coincident with its geometric axis. Also known as two-plane unbalance because correction is required in two planes. This is the most common type of mass imbalance in centrifugal pumps.

E

Eccentric: In contrast to concentric, where circular parts have the same centre, eccentric parts do not have the same centre.
Eccentricity (shaft): The amount that a circular shaft varies from its outer diameter as it rotates with reference to its true centre.
Eddy current: Electrical currents induced within conductive materials by a change in the magnetic field. These eddies have inductance, inducing magnetic fields in the conductive material.
Effective diameter: When referring to metal bellows construction, it is the diameter where the pressure penetrates between the metal plates. This is then used to help determine the hydraulic diameter of the seal face.
Efficiency: The measured power out of a piece of equipment divided by the power produced by the piece of equipment. Always between 0 and 1.
Elasticity: A physical material property in which materials return to their original shape after being deformed.
Elastic range: In material science, when a material is stressed and returns to its original shape, it is said to be in the elastic range of stress.
Elastomer: Derived from the terms “elastic polymer”, is a substance with viscoelasticity. This term is often used interchangeably with rubber. Simply, it is a substance that when released from a stress, returns to its original shape.
Electrical run-out: This results from non-uniform electrical properties of a shaft material. In contrast to mechanical run-out, which eccentricity of the shaft, electrical run-out is non-uniformities within the shaft.
Electrolysis: A chemical reaction caused by ions in liquid carrying an electric current.
End-suction pump: End suction pumps are the most common type of centrifugal pump. End suction pumps have a horizontal shaft with an overhung impeller. The flow goes in the end of the casing, and discharges from the top.
Endurance limit: In material testing, this is the point at which a metal will fatigue without applying any additional stress.
End-user: The ultimate person who is using the equipment. There may be many middlemen in between the manufacturer and end-user, including distributors, third party integrators, etc.
Entrance suction loss: The loss of suction between the inlet of a pump and the impeller.
E.P.A. : Environmental Protection Agency. Governmental agency with a mission to protect human health and the environment.
E.P.R.: Ethylene Propylene Rubber. An elastomer that is a copolymer of ethylene and propylene. Commonly used to seal water based and petroleum based products.
Equivalent length: A way to calculate the friction of fittings, like bends, tees, returns, and valves, in straight run equivalents. Measured in length.
Erosion: Wear and tear caused by the action of the liquid on the materials of the system. If the process fluid has solid particles, the wear will be higher.
External Gear pump: A pump that uses gears to displace the process fluid. The gear or gears are housed in a casing with low clearance. One edge of the gear faces the inlet while the other faces the outlet. When the gear turns, liquid is trapped in the space between the teeth and is thereby moved from the inlet to the outlet.
Expeller: A type of gland seal that reduces the bypass pressure from the pump into the gland or rotary sealing area of the pump. Used in applications pumping slurries. Achieved through a combination of centrifugal force and component tolerances.
Extrusion: Displacement of an O-ring into a gap due to the fluid pressure.
Eye of the impeller: The centre of the impeller, where the process fluid begins its journey outwards to the outlet or discharge.

F

Face combination: The material(s) that is used on the seal faces of mechanical seals. Critical to choose correct material for your application to prevent premature sealfailure.
Face flatness: A measure of how flat a seal face is. As the seal faces are lapped, they must be flat to form a seal and prevent leakage. In this case, flat means less than 300 mm in variation across the seal face. Measured by an optical technique involving an optical flat, a monochromatic light source and interference.
Face lubrication:The lubricant used between lapped seal faces of mechanical seals.
Face pressure: Pressure at the mechanical seal face. This is calculated by summing all the loads on the seal face, including the spring load, hydraulic load and shaft axial thrust and then dividing by the area of the seal face.
Face to faceseals: Two seals in a face to face configuration, where there is a common seal face. In this type of seal, the barrier fluid pressure will always be lower than the stuffing box pressure.
False brinelling: Refers to the removal of material from a ball bearing. In contrast to brinelling, in which the removal happens in one load event, false brinelling happens over time, through corrosion or fretting.
Filled carbon: A carbon that is composed of carbon plus organic or inorganic materials. These extras may not be as robust as the carbon itself, and provide a lower grade carbon, costing less to manufacture and purchase.
Filter: A device that separates liquid from solid. Characterized by the size of particles it can remove from the liquid.
Finite element analysis: A mathematical technique to find approximate solutions to boundary value problems. Used in hydraulics to calculate seal face distortion.
Fire pump:A pump designed specifically to protect from fires. They must meet certain specifications as set out in a code published by a fire regulatory agency. These pumps are then tested/approved by third party agencies. Alternatively,a fire pump may refer to the main pump of a fire sprinkler system.
First critical speed: When increasing in velocity, it is the first speed at which the rotor bearing support system is in a state of resonance. The lowest speed that produces this resonance is the first critical speed. Subsequent increased speeds where this happens are known as the second, third, etc. critical speeds.
Flashing: A rapid change in the state of matter from liquid to gas..
Flatness: When two metal surfaces must seal, the flatness of the surface is important. It is measured by placing an optical flat on the surface, shining a Helium Neon laser through the flat and reflecting it off the surface, and then looking at the resulting interference patterns to identify how flat the surface is.
Flexible-coupled pump: In contrast to the situation in a “Close-coupled pump”, in a flexible coupled pump, the pump and driver each have separate shafts that are coupled through a flexible coupling.
Flexible member: The flexible component of a mechanical seal, contains the spring or bellows.
Flexible rotor:A rotor is flexible if it operates at or near its critical speed. In this case, if a rotor operates at >70%of its critical speed it is flexible.
Flexible shaft: A shaft that operates normally at a speed that is higher than its first critical speed.
Flexibility factor: Ratio of the length of a shaft cubed divided by the diameter to the fourth power. Used to predict whether the shaft will have bending problems.
Floating throat bushing: A bushing that has some radial movement to compensate for shafts that are not true. The bushing is a plain circular ring,usually made of carbon. Because the bushing can move radially it can have less clearance than a fixed throat bushing.
Floating throttle bushing: This is the same as the “floating throat bushing”. In general, the term “throat” bushing is used in low-pressure stuffing boxes and “throttle” bushing refers to the bushing in a high-pressure stuffing box.
Flooded suction: If the pump is below the liquid source, and the suction is fed bygravity. This is a preferred method for centrifugal pumps.
Fluid: A state of material that continually deforms under an applied shear stress. Gas, liquid and plasma are examples.
Fluorocarbon: A term for a compound that contains only carbon and fluorine, bonded together with carbon-fluorine bonds.
Flush: Padding an extraneous source of fluid to the pump’s stuffing box at a higher pressure than the operating pressure of the stuffing box. Mixes with and diltes the process fluid.
Fluting: a term for bearing degeneration caused by electrolysis due to small amount of current that pass through the bearing. When this happens over an extended period of time, and is accompanied by lubricant breakdown, it can cause the bearing to become noisy.
Foot Valve: A valve that prevents loss of priming in centrifugal pumps when the source of process fluid is lower than the pump.
Formed metal bellows: Manufactured by compressing and stretching the metal bellows material. Contrast this with welded bellows.
F.P.M. (fpm): Feet per minute. Used as a measure of speed, or velocity.
Francis vane impeller: An impeller design that is most popular in fans/pumps that operate between 1500 and 4000 rpm.
Free length: The axial length of a mechanical seal before it is compressed.
Fret or fretting: Damage to the inside of the pump or fitting caused by removal of the protective oxide layer from a corrosion resistant material. The rubbing of a softer material against a hard shaft or sleeve causes this. Happens more frequently in low cost seals.
Friction Head: The force (pressure) required to overcome the friction that is solely due to the inside of the pipes/fittings/pumps in a system.
Friction factor f (pipe): The friction factor of piping is a measure of how much frictional force is produced per length of pipe. This will be specific for each type of pipe and will depend also on whether the flow is laminar or turbulent. This factor is required tocalculate the friction loss in a run of pipe.
Friction loss (pump): Friction between the pump and the process fluid results in loss of pressure. Different parts of the pump are more or less susceptible to this force.
Friction (pipe): The force produced as the process fluid flows through the pipes of a system. Caused by movement of the fluid internally as one fluid layer moves against another. Also caused by movement of the fluid against the pipe wall. Rougher pipes will lead to higher friction.
Fugitive emission: Regulatory agencies have declared that some chemicals are harmful to your health. Ifany of these escape into the atmosphere, it’s known as a fugitive emission.

G

Galling: A situation where two moving parts that are in close contact, seize and are bonded together.
Galvanic corrosion: Corrosion due to electrolysis of the anodic metal when two metals in the galvanic series are connected with electrolyte. For example, different stainless steel composites will undergo galvanic corrosion if used to manufacture different components in a pump.
Galvanic series: A way to order metals such that those at the beginning of the series will attack any metal further down the list. The further apart the two metals are in the series, the faster the attack will occur.
Garter spring:A long coiled spring with its ends fused together. It exerts radial force (can be either inward or outward) and is used in shaft seals.
Gasket: A seal between static components in mechanics. Made of deformable material.
Gauge pressure: The pressure exhibited on a dial gauge or on a digital read out from a pressure gauge. This reading indicates the pressure above atmospheric pressure and is usually measured in PSIG (pounds per square inch guage).
Gland: A component of a mechanical seal that attaches to the stuffing box.
Gland follower: In a mechanical seal, it is a part of the stuffing box that is forced against the packing rings to increase radial sealing force
Gland plate (or gland): The plate that connects the mechanical seal to the seal chamber/stuffing box.
Grease seal: A bearing seal that is spring loaded and made of an elastomer, also known as a lip seal. Face seals or labyrinth seals are better choices for pumps.

H

Halogen: A group in the periodic table consisting of five chemically related elements. Fluorine, bromine, chlorine, astatine and iodine.
Hard face: The face of a mechanical seal (rotating or stationary). Usually made from hard materials, e.g. silicon carbide, tungsten carbide, etc.
Harmonic vibration: Oscillations that are periodically sinusoidal.
Hastelloy "C": An alloy chiefly composed of nickel, molybdenum and chromium. Used in mechanical seals due to its corrosion resistance and insensitivity to halide stress corrosion.
Hazen-Williams equation: Is an equation that relates the flow of water in a pipe to the properties of the pipe, and pressure differential caused by friction. Has been superseded by the Darcy-Weisbach and Colebrook equations.
Head: A term in fluid mechanics to represent the energy stored in a fluid due to the pressure exerted on its container. Measured as a length of fluid where a standard of 10m is equal to one atmosphere, or 14.7 psi.
Helium Light Band: When using interferometric methods to measure seal face flatness, the helium light band is used as a measure. It’s length equals 0.0000116 inches or 0.3 µm. Seals are usually manufactured to a tolerance of 3 helium light bands in flatness.
Horizontal pump: A pump where the rotating shaft is horizontal, as opposed to vertical.
Horse power: A measure of power, the rate at which work is done. One horsepower = 746 Watts. Initially adopted to compare the output of steam engines to the power of draft horses.
Hot oil pump: A pump that pumps hot oil. Hot oil is typically between 350 and 800 degrees fareheit.
Hot work: Any type of work that produces an arc, spark, or open flame. For example, cutting, grinding, welding of metal, or similar activity. This work requires a permit and trained personnel.
Hydraulic balance: A means of reducing heat generation in the stuffing box by reducing the seal face area subjected to the closing force.
Hydraulic drawings: Drawings that pertain to the hydraulic systems of the instrument, rather than the mechanical components. In a centrifugal pump, this would include the impeller, the volute, any liquid passageways, suction valves, etc.
Hydraulic force: Depends on Pascal’s principle that the pressure in a closed system is constant. Used to produce larger force in one area of a system by applying a smaller force to a second area of the system.
Hydraulic gradient: All the energy terms of the system (for example velocity head and piping and fitting friction loss) are converted to head and graphed above an elevation drawing of the installation. It helps to visualize where all the energy terms are located and ensure that nothing is missed.
Hydraulic power recovery turbine (HPRT): A turbine that recovers energy from a flowing liquid. It recovers energy by reducing the higher pressure to a lower pressure.
Hydraulic re-rate: Re-rating of a pump by modifying its hydraulic parts. The conditions that are re-rated could include operating capacity, speed, differential head, liquid type, temperature, pressure andsuction among others.
Hydrocarbon: An organic material composed only of hydrogen and carbon.
Hydrodynamic bearings: Ball bearings that use the principle of hydrodynamic lubrication, for example, sleeve bearings and tilting-pad bearings.
Hydrodynamicforce: Force imposed on an object by fluid flowing over or around it.
Hydrodynamic seal: Uses a rotor with grooves to act as a pump and create an air cushion that the opposing sealing face will ride on. Better performance than a hydrostatic seal.
Hydrogen embrittlement: The process by which metals become brittle after exposure to hydrogen.
Hydrogen sulfide (H2S): A highly toxic component of hydrocarbons. Released upon combustion. Pumps that are in use for hydrocarbons containing hydrogen sulfide require special construction.
Hydronium ion: A water with an extra proton, H3O+.Formed by the transfer of an H+from one water molecule to another in extremely acidic conditions.
Hydrostatic seal: This is a type of mechanical seal that balances the opening and closing forces of the seal to maintain a controlled gap between seal faces.
Hysteresis: The dependence of a system not only on its current conditions but also on its past conditions. For example magnetic fields generated by applying an increasing electric current to a ferroelectric material changes the response of the material to the future decrease of that same current.

I

I.D.: Inside diameter.
Impeller: A device that attaches to a rotating shaft and converts the energy of motion, into the fluid being pumped.
Impeller eye: The center of an impeller, also the point at which the liquid enters the impeller.
Impeller eye diameter: The diameter of the opening where the fluid enters the impeller.
Impeller locating ring: A ring concentric with the shaft that prevents the impeller from moving axially. Used to place the impeller on the shaft at the appropriate position
Impeller nut: A fastener, usually threaded and hexagonal that fastens the impeller to the shaft in overhung pumps.
Impeller setting: Open impellers require a clearance between the dishcharge and the volute/back pump plate. It is necessary to set this clearance only after the pump reaches itsnormal operating temperature and must be reset to compensate for wear.
Impeller shroud: A set of plates located on either side of the impeller vanes to prevent solids from entering and damaging the impeller.
Impeller vane: A mechanical component of the impeller that directs the flow of liquid from the eye to the discharge, located at the outer diameter of the impeller.
Impeller vane pass frequency: If an impeller is rotating at 3560 rpm and has 5 vanes, then the impeller vane pass frequency can be calculated by multiplying the number of vanes by the rotational speed of the impeller. In the case above, the result is 17,800.
Implode: The opposite of explode. Bubbles implode if moved to a higher-pressure region of the pump. This can be noisy, damaging the pump's metal parts. Also known as cavitation.
Inboard: The relative position of components in a pump. Inboard refers to components that are closer to the pump coupling, while outboard refers to those further away from the pump coupling. Also known as “inboard side” or “inboard end”.
Inclusion: A non-metallic contaminating piece of material that has become enmeshed in the metal during its manufacture.
Incremental balancing: Balancing a rotor in stages, after adding no more than two major components. Incremental balancing results in a more maintaiable balancing.
Inducer: A small axial vane that is attached to the impeller to reduce the NPSH.
Induction motor: An induction or asynchronous motor is an AC motor in which current is induced in the rotor by a magnetic field generated by the stator by the process of induction.
Inline pump: A pump mounted in a fluid flow system. No separate mounting or base plate is required.
Inside mounted seal: A mechanical seal in which all components are mounted in the process fluid.
Intergranular corrosion: A typeof corrosion in metal where the corrosion between the crystals of the metal are more likely to corrode than the crystals themselves.
Internal gear pump: A pump that uses gears to displace the process fluid. The gear or gears are housed in a casing with low clearance. One edge of the gear faces the inlet as the other faces the outlet. When the gear turns, liquid is trapped in the space between the teeth and is thereby moved from the inlet to the outlet. An internal gear pump differs from an external gear pump, which uses two gears with teeth that both face externally, in that it uses a set of two gears, but one acts as a rotor (large ring gear with teeth facing internally), and the idler, a small gear interior tothe rotor.
Internal recirculation: Loss of efficiency due to the small eddies and recirculating currents in acentrifugal pump.
I.S.O.: International Standards Organization. Sets pump and seal standards for the community. Defines the popular ISO9000 standard for management.
Iteration: Repeating a process and approaching a goal or target. Used to find the asymptote in functions. Very dependent on modern computer algorithms..

J

Jacket: Usually part of a term foreither heating or cooling the stuffing box, known respectively as the heating jacket and the cooling jacket.
Jet: A powerful stream of fluid emanating from an opening.
Jet pump: Jet pumps are commonly found in residential water supplies and use the principle of the venture to produce a low pressure area that acts as a suction for the intake of water/fluid and allows the pump to lift a fluid.
Jig:A guide used in manufacturing to allow a machine tool to accurately cut pieces repetitively.
Jockey pump: A second, smaller pump found in sprinkler systems. It is connected in parallel to the main fire pump and serves to maintain the pressure in the sprinkler system so that when a fire occurs and a sprinkler activates, lowering the pressure in the system, this will be detected by the controller, and the fire pump will be switched on.
Joint: The locations where two pieces are joined together either by welding or a series of flanges and nuts and bolts.
Joule: A unit of measurement of energy. Defined as the energy required to apply a force of one Newton through a distance of one metre.
Journal: The proportion of the main shaft that is supported by a plain bearing.
Journal bearing: A plain, sleeve or sleeve-shaped bearing used to support a shaft.
Journal box: A casing or housing that contains the journal and the journal bearing.

K

Kalrez®: Perfluoroelastomer material used in the manufacture of seals and O-rings. Manufactured by E.I. Dupont, resistant to many different aggressive chemicals.
Kerosene: Combustible hydrocarbon. Also kerosine. Used as a low specific gravity testing fluid after a pump has been shown to not leak water.
Ketone: A chemical group of organic compounds with one carbonyl attached to any of a variety of alkyl groups.
Key: A small square piece of metal that is used to secure a rotating part onto a shaft, preventing the part from rotating independently of the shaft.
Keyway: A slot in the shaft that will accommodate the key.
K factor: A coefficient that provides the friction loss from fittings in a system. Tables exist that list the fittings and their K factors. It is used with the following equation
Kiln: A furnace for drying or baking among other functions. Produces “kiln dried wood” that has dimensional stability used for making patterns.
Kilowatt: One thousand watts. A watt is the SI unit of power, defined as one joule per second.
Kinematics: A branch of mechanics that describes motion of a set of points or bodies, without reference to the force that caused the motion.
Kinetic Energy: The energy an object has due to its motion. In pumps, the impeller imparts kinetic energy to the fluid, which is then harnessed by the resistance created by the volute.
KPa: An SI unit of measurement for pressure. Defined as one Newton per m2. 100 kPa ~ one atmosphere.
KV: Kilovolt or one thousand volts. SI unit of electrical potential difference. The difference that will impart one joule per coulomb of charge that passes through it.

L

Labyrinth seal: A mechanical seal that forces the sealed fluid through a labyrinth like path to slow its leakage.
Laminar: A situation when fluid particles flow in parallel layers and these layers don’t mix.
Lantern Ring: A perforated ring in the middle of a ring set that is used to provide lubricant to packing. Commonly found in the middle of a packing ring set.
Lapping: A method of finishing machined parts that results in extremely flat, smooth surfaces.
Lateral critical speed: The speed at which the lateral deflection of the rotor is in resonance. The critical speed refers to the same property, but it is the speed at which the angular torsional velocity excites resonance in the rotating object.
L10 bearing life: A bearing specification that gives the lifetime of a population of bearings such that after this time, 10% of bearings will have failed due to fatigue failure.
L3 / D4: A metric used to predict how well a pump will perform. L is the length of the shaft measured from the center of the impeller to the center of the radial or inboard bearing and D is the the outside diameter of the solid shaft measured beneath the sleeve. For best performance, this number should be below 60 in imperial units and 2.0 in metric units.
Leakage concentration: How much of the process fluid leaks into the environment. Measured in parts per million.
Leakage rate: A rate (volume/time, e.g. litres/minute) of a fluid that passes through a particular part of the pump, for example a sleeve, seal, etc.
Life Cycle Cost (LCC): Life cycle cost is the total cost of the machinery including purchase, installation, operation, maintenance, repair and dispose of the machinery. Calculated when trying to decide whether to upgrade.
Linear pressure drop: In reference to a mechanical seal, refers to a pressure drop across all lapped faces. Unusual.
Line bearings: Bearings in a pump that position the rotor radially.
Line bored: A method of machining that causes the drilled (bored) holes to all line up.
Liner: A replaceable “liner” that fits into a pump casing to protect it. Often used when the pump processes abrasive material.
Lip Seal: Also known as a radial shaft seal. They are used to seal rotary elements such as a shaft or rotary bore.
LoadE: The total load on a bearing, including both radial, as well as axial loads.
Lobe pump: Similar to gear pumps in operation, except that the lobes do not make contact. Positive displacement pumps that are popular where the sanitary quality is important.
Low flow: Must be taken into account when selecting a pump. Low flow can cause excessive heat build up in the volute.
Low NPSH pump: A pump which has been designed to deal with a low Net Positive Suction Head. Prevents cavitation in the pump.
Lubricant: An introduced substance that reduces friction between moving parts. Usually a fluid.

M

Mach number: Relates the speed of a moving body in a fluid to that of sound. As this is a ratio, it’s a dimensionless number.
Magnetic drive: A sealless pump that uses a motor coupled to the pump by magnetic means rather than a direct mechanical connection.
Magnetic pickup: A sensor that transduces a varying magnetic field into an AC signal. Used to determine the speed of rotating metallic objects by detecting variations in the magnetic field as the object rotates.
Magnetic seal: Seals that use magnetic force rather than springs to provide sealing pressure.
Magnetite: Iron oxide ( Fe3O4). A coating that forms in iron pipes. Protects the pipes, but can be very destructive to seals and their components.
Mating ring: A.k.a. the hard face of a mechanical seal.
Mean Diameter: The average diameter.
Mechanical seal: A device that joins fluid-mechanical systems together by preventing leakage between the systems.
Mercury (Hg): An element that is both a metal and a liquid at room temperature.
Metal bellows: Some mechanical seals use these in place of elastomers.
Metal fatigue: Progressive structural damage that occurs through repeated loading of a metal part. .
Micro Organisms: Biologically active organisms used in a variety of biochemical processes. Can cause corrosion if not controlled.
Minimum continuous stable flow (MCSF): The lowest flow at which a pump can operate within the specifications (noise, vibration, etc.) set forth by a user.
Minimum flow: See “low flow”. A condition which causes excessive heat to build up inside the pump casing.
Minimum NPSHA: The minimum net positive suction head available. This quantity should be larger than the NPSHR or the NPSH required.
Miscible: Refers to the ability of one liquid to mix with another. Water and oil are not miscible, but water and ethanol are.
Mixed flow pump: A pump that uses both centrifugal force and lift produced by the impeller to move a fluid.
Modulus of elasticity: Also known as Young’s modulus. A physical property of a material that is a measure of stiffness of an elastic material.
Moment of inertia: A property of rotating objects that describes their resistance to change in angular momentum.
Momentum thrust: As the process fluid enters the pump and is acted on by the impeller it changes direction and therefore the impeller imparts a momentum thrust upon the fluid.
Monochromatic light: Light exists as wavelengths of colours from purple (~400nm wavelength) to red (~640nm wavelength). White light is a mixture of all wavelengths, whereas monochromatic light is light of a single wavelength.
Motor frame: NEMA (National Electrical Manufacturers Association) publishes standards for sizes of electrical motors. The Motor frame is a quantity that comes in the published sizes.
Multistage pump: Any pump with more than one impeller. Typically pumps with two impellers are referred to as two stage pumps.

M

Negative pressure: In reference to one atmosphere. Anything less than this number is negative.
Newton: The SI derived unit of force. Because Force equals mass times acceleration, the Newton is equal to 1 kg *m/s2.
Newtonian fluid: A fluid that behaves without changing its viscosity as a function the rate of flow.
Non-Destructive Examinations (NDE): A process which pumps or pump components are examined for defects without resulting in the destruction of the component being examined. A.k.a. Non-destructive testing (NDT).
Non lubricant: In contrast to a lubricant, this type of fluid does not act to reduce friction of moving parts against each other.
Non-Newtonian liquid: In contrast to a Newtonian fluid, this type of fluid has a viscosity that changes as a function of flow rate, or shear stress.
Normal operating point: This is the set of conditions at which the pump normally operates. It could be the same or different than the best efficiency point or the rated operating point.
Nozzle head: The part of a pump where the fluid is discharged. Commonly reduced diameter causes the fluid to exit the system faster than its flow through the system.
N.P.S.H.A: The net positive suction head available that can be used to prevent cavitation within the pump. It is defined as static head plus surface pressure head minus the vapour pressure of the process fluid minus the friction loss due to the piping, valves and fittings.
N.P.S.H.R.: Net positive suction head required to keep a pump from cavitating. A characteristic of the pump. Calculated by the manufacturer with cold water.

O

O.D.: Outside diameter.
O.E.M.: The company that makes the product, not the company that distributes it. Acronym that stands for Original Equipment Manufacturer.
Oil analysis: A preventative maintenance procedure in which a lubricant’s properties are analysed in a laboratory to check for particles, water and wear debris.
Oil life: The working life of a lubricant. Oil will maintain its useful properties for about 30 years at 30°C, if not contaminated.
Oil mist: A system where oil is atomized with air and subsequently sent into the pump bearings.
Oil whirl: This can occur in bearings that are lubricated hydrodynamically. It’s an instability caused by a sudden disturbing force to the shaft being supported by the bearing and causes an eccentricity to occur by an increased amount of oil on one side of the shaft compared to the other.
Open free flow: When the discharge pipe or hose is fully open at the end with no restrictions.
Open impeller: An impeller with vanes attached to the hub with no front or back shrouds; the impeller may have small web in-between vanes for structural support.
Operating length: The length of a seal when it is in operation, i.e. while it is under compression.
Operating point: The point on the pump performance curve at which a pump operates. It corresponds to the flow rate and total head sustained by the pump.
Operating region: Refers to the range in pump performance curve in which the pump operates.
Optical flat: A very flat (usually ¼, 1/10th or 1/20th of a wavelength variation across its surface) piece of glass used in combination with light to measure the flatness of test pieces.
O-ring groove: The machined slot on a piece of metal or elastomer where an o-ring is inserted. Forces the O-ring to stay in a set position.
OSHA: Occupational and Safety Health Act. Governmenatal regulations that impact the workplace. Designed to keep workers safe.
Outboard: A reference to the position of something with respect to the pump coupling. Outboard is further away from the pump coupling, while inboard is nearer.
Over hung impeller: An impeller on a shaft that is supported on one side only.
Overhung pump: A pump whose impeller shaft is supported by bearings on one side only. Also known as a cantilevered pump.
Overrunning clutch: A clutch that engages in only one direction. Also known as a “freewheel”. Most bicycles have overrunning clutches on their rear wheels.
Oxidizer: A chemical that reacts with carbon to form an aggressive compound. Will attack most metallic components inside a pump, including seal faces, etc.
Ozone: A variant of Oxygen with 3 Oxygen atoms instead of two. This makes it highly reactive. Is formed by electric sparking (e.g. by electric motor brushes).

P

Packing: A manner in which to stepwise reduce the pressure from the pump so that by the time the fluid gets to the last step, the amount of leaking is acceptable. Usually implemented as a set of rings to produce the pressure gradient.
Packing ring: A seal composed of a set of rings that prevents leakage of the fluid into the atmosphere.
Parallel operation: As opposed to Series operation. Two pumps are connected to the same head and thereby provide twice the flow rate as a single pump.
Partial emission pump: Also known as a vane pump. A pump designed to handle corrosive chemicals at low flow rates. Developed in WWII to pump fuel into German Ram jet engines.
Pascal: The SI derived unit of pressure. Equivalent to one Newton/m2. 1 atmosphere of pressure is equal to a little over 100KPa.
Passivated: A metal surface is said to be passivated when it has a protective oxide layer formed on its surface.
Pattern: Usually a wooden pattern to make a mold used for metal castings.
P.D. Pump: Positive displacement pump. Pumps up to very high pressure, but low flow rates.
Performance curve: A graph depicting the plot of total head vs flow rate for a specific pump, with a specific impeller and set of characterisitics.
Peripheral (regenerative) pump: Also known as regenerative or regenerative turbine pump. An alternative design to a centrifugal pump. In these pumps, fluid passes through the vanes many times (instead of once, in a centrifugal pump). The impeller has short vanes at the periphery and these vanes pass through a ring shaped channel. The fluid enters between two impeller vanes and is set into a circular motion, this adds energy to the fluid particles which travel in a spiral like path from the inlet to the outlet. Each set of vanes continuously adds energy to the fluid particle.
Peripheral speed: The velocity, or speed, at the periphery of some diameter (see peripheral velocity).
Peripheral velocity: Same as peripheral speed.
pH: The measure of how many H+ ions or OH- ions are in solution. The scale is logarithmic and ranges from 0 (very acidic) to 14 (very basic).
Pickling: A process that cleans metals by immersion in a bath of nitric and hydrofluoric acids. The acids remove any impurities on the surface.
Pipe friction loss: The loss in head due to the friction between the process fluid and the walls of the pipes and joints.
Pipe roughness: A measurement of how rough the inside surface of a pipe system is. Many measurements are taken and averaged. It is the average size of peaks that are on the internal surface of the pipes producing friction.
Pipe strain: Pipe strain is the strain on the colute of a pump due to the piping attached. It can cause mechanical seal failure.
Piping pressure (maximum): Pipe systems have a maximum pressure rating to which they may be subjected. Otherwise they may burst due to excessive pressure. This also includes joins and flanges. The ASME pressure piping code B31.3 provides the maximum stress for pipes of various materials.
Pitot pump: A pump that contains a rotating casing that causes the fluid to rotate. At one point within the rotating cyclinder of fluid, there is a pitot tube, or pick up tube that captures a small amount of the rotating fluid and sends it to the discharge under high pressure.
Pitting: Erosion at the surface of a material as pits due to corrosion, erosion or cavitation.
Pitting Resistance Equivalent Number (PREN): A characteristic given to a material that indicates how resistant the material is to pitting corrosion. Higher numbers indicate a greater resistance to pitting corrosion.
Plan 11: A mechanical seal single seal piping plan referenced by API 682, ISO 21049, and ASME B73.1& B73.2, for single seal arrangement using the pump liquid as medium. Plan 11 flush line originates at the pump discharge, or at a point on the pump casing where the pressure is higher than that at the seal chamber, and is piped through a flow control orifice to the flush port on the seal flange or seal chamber tap. The liquid flushes the seal face, flows around the seal, exists through a pressure reducing throttle bushing, and flows back into the impeller suction area.
Plastic range: Metals have an elastic range, where they “remember” what shape they were before you moved them, and a plastic range, where they won’t remember their prior shape.
Positive displacement pump: A type of pump that causes a fluid to move by trapping a fixed amount of the fluid and moving it into the discharge pipe.
Pour point: The temperature at which liquids cease to flow.
Power end: The section of a pump that attaches to the power source. Bearings are found here.
Power factor: In an AC circuit, the relationship between the real power flowing to the load and the apparent power in the circuit.
Precision bearing: Ball bearings and roller bearings are precision bearings, while sleeve bearings are not.
Press fit: Graphite, because of its softness, can be pressed into any irregular shaped holder and it will shear to fit the holder.
Pressure: Is the ratio of a force over an area over which the force is applied.
Pressure drop: The difference in pressure between two areas of a pump, or between the inside and outside of a container.
Pressure gradient: The pressure drop, when referring to mechanical seals, across the mechanical seal faces.
Pressure head: The pressure at the pump experted by atmospheric and other additional pressure that might be in the vessel.
Prime: In a centrifugal pump, if the source is lower than the pump, a small amount of process fluid is infused into the pump to start the suction process.
Progressive cavity pump: A positive displacement pump. Ideal for fluids with high viscosity (e.g. grease, pastes, etc.) They are also known as eccentric screw pumps.
Propeller pump: A.k.a. axial flow pump. A pump in which the impeller imparts lift to the fluid propelling it along due the impeller’s shape.
Pseudoplastic: Any fluid whose viscosity increases slowly with the rate of shear is said to be pseudoplastic.
PT factor: A factor given to gaskets consisting of the operating pressure multiplied by the operating temperature at which the gasket can be safely used.
Pump curve: A graph supplied by the pump manufacturer depicting the relationship between the head and the capacity of a particular pump. Usually contains different curves for different sized impellers.
Pumping ring: In a mechanical seal to provide circulation between two mechanical seals. Required if oil is the barrier fluid, due to the oil’s poor specific heat.
Pump out vane: A feature of some impeller designs that lowers the stuffing box pressure.
Pumps as turbines (PAT): A pump running in reverse. That is, the fluid inside the pump moves and causes the pump to rotate.
Pure oil mist lubrication: A lubrication system for bearing that uses an oil mist, rather than a liquid in a sump.
Purge oil mist lubrication: A lubrication system where an oil mist purges only the bearing housing.
Pusher seal: A low quality design that uses a spring-loaded dynamic elastomer.
P.V. Factor: A correlation between the pressure and the velocity at mechanical seal faces. The correlation does not hold up.

Q

Q: Commonly used as a symbol for flow rate (quantity). Units may be expressed as any volume per unit time.
Quadrant: Referring to 1/4th of the circumference of a circle, spanning 90°.
Quadratic: A polynomial equation where the unknown is raised to the power of 2. For example: 9x2+3x+1 =4.
Quality control: A business process to verify and maintain a desired standard of quality in a product or production system.
Quench: Adding fluid outside the seal to either cool the seal, or to dilute any product leaking out of the seal face.
Quill shaft: A shaft that is hollow, containing another shaft inside of it.

R

Radial: Arranged like radii. Arranged along the radius of a circle, in this case, the circle refers to the circular shaft.
Radial bearing: Most bearings are meant to support radial loads. Whether they can support axial loads depends on the type of bearing.
Radial flow pump: A centrifugal pump designed so that the pump has medium head and medium flow, or high head and low flow.
Radial split pump: A pump that has its case split along a line that is perpendicular to the centerline of the shaft.
Radial vane pump: Also known as partial emission pump. A pump designed to handle corrosive chemicals at high head, with low flow rates. Developed in WWII to pump fuel into German Ram jet engines.
Rated operating point: The point on the pump efficiency curve at which the pump vendor guarantees the pump’s performance.
Reaction bonded: A method of manufacturing silicon carbide by a reaction between porous carbon (graphite) and molten silicon.
Recessed impeller pump: Sometimes known as vortex pump. A pump design which reduces contact between the impeller and the process fluid by recessing the impeller. Ideal for slurries containing solids or fibres.
Recirculation: Refers to the fact that at both high and low flow (as compared to the BEP on efficiency graph), the process fluid will tend to recirculate at the suction and discharge.
Relative density: Ratio of a liquids density to that of water measured at 4°C. Also known as specific gravity.
Renkin scale: A temperature scale with the same size units as farenheit, but starting at 0° defined as absolute 0.
Repeller: An additional impeller used to lower the stuffing box pressure.
Residual unbalance: The amount of unbalance (in terms of mass) remaining after a rotor, or shaft, has been balanced on a balancing machine. Expressed as ounce inches. This will cause the rotor to vibrate during operation. The magnitude depends on the amount of unbalance and the rotor speed.
Reynolds number: A dimensionless number that relates the ratio of inertial forces (velocity) to viscous forces.
Rheopectic: A fluid whose vicosity increases with time.
Rigid rotor: A rotor that operates at less than or equal to 70% of its first critical speed. Does not vibrate.
Rigid shaft: A pump shaft that operates below its critical speed..
RMS: Root mean square. A statistical measure of the magnitude of variation in some quantity.
Rockwell "C": A scale used to measure hardness of materials.
Rotating seal: In mechanical seals, if the moveable portion of a seal rotates with the shaft, then the seal is said to be a rotating seal.
Rotor: The compilation of all the rotating elements in a pump. Includes the shaft, the impeller, wear rings, bearings, etc.
Run out: If the rotating shaft doesn’t rotate exactly on its centerline, then the run out is a measure of the deviation from true rotation. Expressed as twice this distance.
Runner: Historical term for the impeller, rarely used.

S

Sag boring: A machining techniques that bores components with a slight eccentricity to compensate for the natural sag of a rotor due to gravity. Usually used on casing wear rings and center rings to prevent the rotating parts from rubbing with the casing stationary wear parts during start-up or coast down.
Screw impeller: An impeller that is the shape of a screw. Used to pump liquids with high percentage of solids. Originally developed to pump liquid containing fish.
Seal faces: The metallic faces (lapped so they are very flat – to within a few hundred nanometers across their entire surface) in a mechanical seal that form the seal.
Sealless pump: A specially designed pump that is used to pump dangerous liquids. It prevents them escaping into the atmosphere because the internal rotor is assembled with the impeller and does not extend outside the casing.
Seal life: The life expectancy of a mechanical seal. Seals should last until the sacrificial (usually carbon graphite) is worn away.
Seal only pump: A pump that contains only seals and no soft packing, due to the fact that it has no conventional stuffing box.
Self align: Some seals are designed to align with the shaft exactly by built in mechanisms.
Self-priming pump: A pump that contains a reserve amount of process fluid that helps to create an initial vacuum and lift fluid from the source.
Self sintered silicone carbide:. One form of Silicon Carbide. To bond SiC powder into ceramics, the powder is sintered. At temperatures above 1700°C, the alpha form of SiC is formed.
Self-venting pump: A pump in which the suction and discharge control valves can be opened to flush trapped gas during or prior to the start up sequence. API Standard 610 considers a pump to be self-venting "if the nozzle arrangement and casing configuration permit adequate venting of gases from the first-stage
impeller and volute area to prevent loss of prime during the starting sequence."
Semi-open impeller: An impeller with no front (suction) shroud. Used typically when pumping particle containing fluids.
Series operation: As in electricity, this is the case when two pumps are connected such that the discharge of the first pump feeds into the suction of the second pump. Care must be taken to match the discharge of pump 1 with the intake of pump 2, otherwise overheating or cavitation can occur.
Shaft: The component of the pump that transmits the radial force from the motor to the impeller.
Shaft flexibility factor (SFF): A dimensionless number, characterizing the relative stiffness of a shaft or rotor. SFF is calculated using the formula SSF = (L3 ) / (D4). Where L is the length of the shaft and D is the diameter. Can be used to compare shafts.
Shaft packing: Seals are expensive, so manufacturers supply their pumps with soft packing to seal the shaft. Mechanical seals then replace the shaft packing.
Shaft sleeve: A thin cylindrical, metal sleeve placed around the shaft to prevent wear and tear.
Shelf life: Refers to the length of time a component will perform as intended by the manufacturer. Some elastomers (notably Buna N) have short shelf lives due to their breakdown when exposed to air and ozone.
Shore "A": A scale used to measure hardness of materials. Defined by Albert Shore in the 1920s.
Shut-off head: The shut off head is the head (pressure) delivered by the pump with the discharge valve closed (shut off).
SiC: Silicon carbide. Very hard and durable, therefore commonly found in seal faces.
Side channel pump: Is a specially designed pump that provides high head at low flows. Ideal for liquefied gases, as the pump can pump liquids with up to 50% gas.
Single plane balancing: Also known as static balancing. The process of balancing an impeller in a single plane only.
Single stage pump: A pump with a single impeller. Compare to two-stage and multistage pumps.
Single suction pump: A pump with a single suction impeller, either the first impeller in a multi-stage pump or the only impeller in a single stage pump. See double suction pump.
Single suction impeller: An impeller with a single inlet. The liquid enters from the side only. Mixed flow and axial flow impellers are always single suction type.
Sintered material: Manufactured from a powder rather than melted and poured into a mold, or formed.
Siphon: A pipe or pipe system that allows the liquid to flow uphill. Powered by the fact that the discharge point is lower than the surface of the inlet reservoir.
Skidding: This term refers to the manner in which an impeller skids along debris or solids along the bottom of a pump.
Sleeve bearing: A type of non-precision bearing. Usually a tube that fits around the shaft composed of metal or teflon.
Slip stick: Mechanical seal faces that alternately slip, then stick. Usually caused by poor quality lubricant.
Sludge pump: A pump design that prevents solids in a liquid from settling within the pump.
Slurry: A mixture of liquid and solid.
Slurry pump: A heavy duty pump designed to withstand the corrosive or abrasive effects of particles in the process fluid. Achieved by lining the pump with extra material that can withstand the assault.
Soft foot: Centrifugal pumps that are manufactured such that one of the feet on the pump has a tendency to rise when not bolted down. Makes it difficult to balance and align the system.
Soluble: When one compound (liquid or solid or gas) is dissolved into a second liquid compound, the first is said to be soluble.
Spalling: Damage to bearings caused by improper lubrication, mechanical damage, defect or fatigue.
Span: Distance across something. The distance from an inside radius to an outside radius, the distance from the shaft to the volute, etc.
Specific Gravity (SG): The ratio of the density of a substance compared to the density of a reference (usually water at 4°C).
Specific heat: The heat capacity per unit mass of a given material. The heat required to change the temperature of a specific mass of the material (e.g. 1g) by a given amount (e.g. 1°C).
Specific speed: A dimensionless number used to characterize turbomachinery. Normalises impellers to a speed in revolutions per minute to that of a geometrically similar impeller if it were to deliver 1 gallon per minute against 1 foot of hydraulic head.
Speed of sound: How fast sound travels. Differs in different media. In air at sea level it is 340.3m/s.
Speed-torque curve: A graph of a pump’s speed versus its torque.
Spool piece: A prefabricated section of piping including the pipe, fittings and flanges.
Spring force: The force supplied by the spring on the seal faces.
Standard volute pump close coupled: In this type of pump, the impeller is connected directly to the drive shaft.
Standard volute pump separately coupled: In contrast to a close coupled situation, a separately coupled pump is one in which the impeller is connected to the drive shaft through an intermediate shaft with couplings.
Stainless steel: An alloy of steel that contains a high percentage of chromium. Reduces oxidation.
Static head: The maximum height (pressure) that a pump can deliver.
Stationary seal: Refers to a mechanical seal where the spring loaded portion of the seal does not rotate with the shaft.
Strainer: A metal screen installed at the inlet of a pump to prevent foreign bodies from entering the pump.
Stuffing box: An assembly of mechanical components that houses a gland seal. Prevents leakage.
Stuffing box pressure: Pressure in the stuffing box. Varies widely depending on pump design.
Standby service: A service where a piece of equipment is in a state from which it can be immediately used for operation, either replacing a faulty component of sharing the load.
Static balancing: A.k.a. single plane balancing. The process of balancing an impeller in a single plane only.
Stiffness ratio: Another name for L3/D4, the ratio of the cube of the length of a shaft to the 4th power of it’s diameter. An indication of the stiffness of a shaft.
Strain: The deformation of a material caused by an applied stress.
Stress: The measure of the forces that particles are exerting on one another in a material.
Stress relief: To remove the residual stress from a component. Important in lapped seal faces.
Stress corrosion cracking: The process of metal undergoing fracturing when it is under tensile stress. Other examples include chloride attack of austenitic stainless steel and caustic embrittlement of cast irons and carbons.
String test: A test of the entire pumping package supplied by a vendor. Usually defined in the purchase contract. Includes all components of the system.
Submersible pump: A pump that operates when it is completely submerged. Must have waterproof electrical circuits and is usually liquid cooled.
Submersion: Submersion refers to the height difference between the surface of the intake reservoir and the opening of the pump intake pipe.
Suction bell: A bell shaped tubular section at the inlet of a vertical lineshaft pump. Used for directing the flow of liquid into the impeller inlet.
Suction case: A bell shaped tubular section at the inlet of a horizontal pump. Used for directing the flow of liquid into the impeller inlet.
Suction flow splitter: A piece of metal across the intake of certain pumps to force the liquid into a laminar flow.
Suction guide: An extra mechanical device that helps to produce laminar flow in situations where the piping just before a pump contains a 90° bend.
Suction head: Suction head is the term for the head due to the fact that the source of the pump is above its centerline.
Suction lift: Opposite of suction head. Occurs when the source for the pump is below the pump’s centerline.
Suction line: The suction line of a pump system is piping which transports fluid material from its source to the pump itself.
Suction recirculation: A system to reduce pressure in the stuffing box by recirculating some of the discharge back into the stuffing box.
Suction specific speed: A number that will help to determine what type of geometry to use for maximum efficiency, but prevent cavitation.
Suction Static Head: The height difference between the surface of the inlet reservoir and the centerline of the pump. If the tank is pressurized, this pressure is also included.
Suction Static Lift: A.k.k. suctions static head. Only occurs when the pump is above the inlet reservoir.
Surface speed: A measure in linear terms (feet per minute) of how fast a component that is moving radially is moving.
Swamee-Jain equation: An equation that can be used as a substitute for the Colebrook equation for calculating the friction factor f.
Synchronous motor: Seldom used in pumps, but often in elevators or compressors. Pumps typically use “squirrel cage” motors.
System: The total set of components is referred to as the system. In a pumping system, this would include piping and mechanical equipment from the inlet point to the discharge. as in pump system.
System Curve: A graph depicting the pump’s total head vs flow. It is used to estimate how the pump will perform at different flow rates. The Total head includes the static head (constant) and the friction head and velocity head difference – and these depend on the flow rate. The intersection of the system curve with the pump characteristic curve defines the operating point of the pump.
System head: The head (pressure) cause by friction along the pipe walls and due to the joints in the system..
System requirements: The set of conditions (velocity, elevation difference, pressure, etc) that define or determine the total head.

T

Tandem seals: Two mechanical seals facing the same direction with low pressure barrier fluid in between them.
T.D.H.: Total Discharge Head. The sum of the static (differential) head and friction loss.
Tensile strength: The tensile strength is the force required to break something as it is being pulled apart axially.
Test baseplate: A specially designed support used during performance testing of a pump in a test well.
Test curve: A graph depicting the results of a performance test.
Thermal conductivity: A property of a material that designates how well the material can conduct heat.
Thermal imaging: Using an infrared (heat) sensitive camera to image machinery to find where the hotspots are.
Thermoplastic: A plastic material that can be melted over and over again without changing its properties. Used in injection molded plastics.
Thermosetting: Unlike a thermoplastic, this material can only be melted once. After it has cooled and set, it cannot be re-melted without losing its properties.
Thixotrophic fluid: A fluid whose viscosity decreases with agitation. E.g non-drip paint.
Thrust: Refers to the axial movement of the rotor. At start up the thrust can be axially in either direction depending on the balance of the rotor/impeller assembly.
Thrust bearing: A bearing that takes an axial load and locates the rotor axially.
T.I.R.: Total Indicator Runout (see below).
Torque: The tendency of a force to rotate an object around an axis.
Torr: A traditional unit of pressure. Historically equivalent to one “millimeter of mercury” in a barometer.
Torsional critical speed: The resonant frequency associated with the torsional deflection of a rotor. Different than later critical speed.
Total Dynamic Head: This term has been replaced by and is equivalent to “Total Head”.
Total head: The sum of the head produced by the pump. It can be calculated by subtracting the suction head from the discharge head.
Total Indicator Runout (T.I.R.): The runout (a non-true shaft is said to have “runout”) measured manually on a dial indicator.
Total Static Head: The discharge pressure minus the suction static head – including the difference between the surface pressures of the two (discharge & suction) tanks, if they are pressurized.
Transducer: A device that turns a mechanical (e.g. vibration) movement into an electrical signal that can be read or saved.
TransferringTo move a substance, usually a liquid, from one place to another.
Trip speed: A speed that “trips” an automatic shutdown of a pump to prevent damage by being overloaded.
Tungsten carbide: An inorganic compound made of equal parts tungsten and carbon. Roughly three times harder than steel. Used as a common hard face seal material due to it’s durability.
Turbulence: In fluid dynamics, this is non-laminar flow.
Turbulent: In fluid dynamics, this is a characteristic of fluid particles that are not undergoing laminar flow, but are generally flowing in one direction, but may go in any direction.
Two plane balancing: Removing residual unbalance in a rotor/impeller system by balancing in two planes rather than one.
Two-stage pump:A pump design containing two impellers operating in series. The discharge of the first stage is the input of the second stage
Two way balance: A method for balancing seals in two directions.

U

Unbalance: Referred to with respect to rotating parts in mechanical systems. If these parts have an uneven mass distribution, this will cause vibration as the part rotates. The vibration is directly proportional to the speed of rotation and the amount of unbalance. See residual unbalance.
Unbalanced seal: Seals with a balance ratio > 1. The balance ratio is defined as the ration of the closing area to the opening area of the seal faces.
Undercut, or undercutting: Reducing the effective diameter of an impeller by trimming the vanes, while leaving the shroud intact.
Underfile, or underfiling: Changing the impeller vanes by hand grinding some metal off of them. This will change the pump’s performance by reducing the vane thickness and increasing the area of opening between adjacent vanes.
Unfilled carbon: Pure carbon, containing no impurities. Filled carbon has other components that may react with process fluid, if used to manufacture seal faces.
Unfiltered vibration: Vibrations can occur at many different frequencies. Unfiltered vibration refers to the entire spectrum of possible vibrations, while filtered vibration refers only to those specific frequencies selected.
Upstaging: The addition of impellers to a multi stage pump that has been previously de-staged.
U.S.C.S.: A system of measurements commonly used in the United States. Acronym that stands for: United States Customary System.

V

Vacuum: A pressure of less than one atmosphere.
Vane passing syndrome: Cavitation caused by the clearance between the impeller and the cutwater being too small.
Vane pump (hydraulic): A positive displacement pump that consists of vanes mounted on a circular rotor. The rotor sits inside a circular cavity. These two circles are offset, to create eccentricity.
Vaporize: Fluid changes state from liquid to gas.
Vapor pressure: If a liquid is in a chamber that is below the vapor pressure, then the liquid will vaporize.
Variable speed motor: Can be used to control flow in the system by varying the impeller speed.
V.D.M.A.: The German Engineering Federation. It’s the trade association for the German mechanical engineering industry.
Velocity: Typically used to mean speed, but also includes directionality.
Velocity head: The energy contained in a flowing fluid. Its kinetic energy. Calculated by the term (velocity)2 /2 (acceleration of gravity).
Vent: To remove air or gas from a mechanical system.
Venturi (Bernoulli's law): A pipe that has a section in its middle of smaller diameter than either end. The pressure in this area will be less than the pressure in the area of piping with the larger diameter.
Vertical canned pump: A vertical pump that has a double casing composed of an inner bowl and an outer barrel. The outer barrel, under full discharge pressure, compresses the liquid in the inner bowl.
Vertical pump: Any pump where the shaft is mounted vertically.
Vibration Damping: Important in mechanical seal design to prevent seal faces from opening and leakage occurring.
Vibration spectrum: A plot of amplitude of vibration vs frequency. Sometimes this is referred to as a vibration signature and it can be used to identify the source, or cause, of high vibration levels in turbomachinery.
Viscosity: Resistance to gradual deformation of a fluid by shear or tensile stress.
Viscous drag pump: A pump design that uses a flat impeller containing no vanes. The fluid is moved by interacting with the flat disk of the impeller through its viscosity.
Viton®: An elastomer brand name manufactured by E.I. Dupont Dow. Generically known as a fluorocarbon.
Volute: A spiral shaped container that houses the impeller. Its function is to collect and direct the flow of liquid coming out of the impeller.
Volute casing: Converts energy from the velocity of a fluid into pressure by using the venture effect.
Volute insert: An insert welded at the volute lip to change the pump performance. It’s a new technology used to effect reductions in capacity of re-rated pumps.
Volute pump: A pump design where the casing is shaped like a volute (spiral). Can contain either a single lip or two lips.
Vortex: A mass of liquid in rotary motion around an imaginary axis. The flow is referred to as vertical flow.
Vortexing liquid: Refers to the inlet where a liquid that is vortexing, may draw air into the intake.
Vortex Pump: A pump used in applications where a very large percentage of solids are contained within the fluid. Operates by having a recessed impeller that is out of the flow path.

W

Water hammer: Occurs in a piping system due to rapid fluctuations in pressure. Usually caused by change in pump conditions, or the opening or closing of a valve too rapidly.
Water Horse Power (W.H.P.): The horse power equivalent of the pump calculated by using the following formula = head x gpm/3960.
Water NPSHR: The net positive suction head (NPSHR) required. This is the suction required by a pump when it is pumping water. It is used as baseline value for estimating its NPSHR when pumping other types of liquid.
Watt: A measure of work. The rate at which work is done when an object’s velocity is held constant against an opposing force of one Newton. (Units are Newton meters/second).
Wave spring: A special washer that is used in mechanical seals when axial space is at a premium.
Wear ring: Restricts leakage from the discharge to the inlet on closed impeller pumps and should be replaced when the recommended clearance is doubled.
Welded metal bellows: A mechanical seal design that uses metal instead of elastomer. Excellent for cryogenic and hot applications.
Wet critical speed: API 610 d The critical speed of a rotor that includes the consideations of the pumped fluid. Compare to dry critical speed.
Wet end: The components of the pump that get wet from pumping the fluid. Stuffing box, impeller, volute, etc.
Wetted surface: Any of the internal surfaces of a pump that comes into contact with the process fluid.
Wobble plate: A plate that attaches to a rotating component to reduce vibration at high speeds by correcting the balance.

X

Sorry... There are no pump terms for the letter 'X'.
But if you have one, please let us know and we will add it in.

Y

Y-axis: The vertical axis in the Cartesian coordinate system.
Yield point: The point of transition for a metal when it goes from an elastic material (returns to its starting shape) to a plastic material (does not return to its starting shape).
Young's modulus: The measure of the stiffness of an elastic material. Defined as the ratio of the stress along a particular axis over the strain along the same axis.

Z

Z: A symbol used in pumping to indicate a pump’s hydrodynamic size.
Zero percent head loss NPSHR (NPSH0): The lowest NPSHR by a pump that results in zero head loss from the performance curve when tested with enough NPSHA.
Zymaxx: The trade name for a composite material containing carbon fibers. Used to make pump components such as bearings, wear ring inserts, bushings, etc.

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