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Glossary of pump terms: A

Absolute pressure: The absolute pressure is the sum of the gauge or dial pressure and the atmospheric pressure (14.7 psi). 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 centre line of the pump shaft with the centre line 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.

Anodise: A treatment used in particular on aluminum. The treatment adds a heavy layer of protective oxide coating.

ANSI 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.

API 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”.

API 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 ANSI 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.

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