Pump Terminology

Air-Lock

Air trapped at high points in piping that has dips, usually due to horizontal piping arrangements having excessive dog-legs.

Cavitation

Process in which small bubbles are formed and implode violently, occurs when the inlet pressure falls below the vapor pressure, NPSHa < NPSHr.

Dead Head

The ability of a pump to continue running without damage when discharge is closed off. Only recommended for less than one minute.

Discharge Head

The outlet pressure of a pump in operation.

Flooded Suction

Liquid flows to pump inlet from an elevated source by means of gravity. Recommended for centrifugal pump installations.

Flow

A measure of the liquid volume capacity of a pump.

Packing Seal

The packing material is held in place by the stuffing box gland and compressed to form sealing against the shaft. During operation tightening the glands may be required to prevent leakage. It is important to do this gradually and evenly to avoid excessive shaft friction.

Self-Priming

Pumps that draw liquid up from below pump inlet (suction lift), as opposed to pumps requiring flooded suction.

Strainer

Device installed in the inlet of a pump to prevent foreign particles from damaging the internal parts.

Sump

A well or pit in which liquids collect below floor level; sometimes refers to an oil or water reservoir.

Total Head

Sum of discharge head minus the suction head.

Fluids

Include liquids, gases, and mixtures of liquids, solids, and gases. The terms fluid and liquid are both used to mean a pure liquid or a liquid mixed with gases or solids that acts essentially like a liquid in pumping applications.

Head

A measure of pressure, expressed in meters of head for centrifugal pumps. Indicates the height of a column of water being moved by the pump.

NPSHr – (Net Positive Suction Head Required)

Determines the required suction head (maximum suction lift). It is inherent to the design of the pump and is measured in meters of water.

NPSHa – (Net Positive Suction Head Available)

Is determined by the pipe system on the suction (inlet) side of the pump.

Pressure

The force exerted on the walls of a tank, pipe, etc., by a liquid.

Prime

Charge of liquid required to begin pumping action when liquid source is lower than pump. Held in the pump by a foot valve on the intake line, or by a valve or chamber within the pump.

Seal Chamber/Stuffing Box

A chamber, either integral with or separate from the pump case housing that forms the region between the shaft and casing where sealing media are installed for the primary function of protecting the pump against leakage. When the sealing is achieved by means of a mechanical seal, the chamber is commonly referred to as a Seal Chamber. When the sealing is achieved by means of a packing, the chamber is referred to as a Stuffing Box.

Seals

Devices mounted in the pump housing and/or on the pump shaft that prevent leakage of liquid from the pump. (See Mechanical Seal / Packing Seal training)

Mechanical Seal

Eliminates the problem of excessive stuffing box leakage by means of a rotating seal assembly affixed to the pump shaft. A static seal is formed between the two seal faces and the sleeve. When a seal wears out causing intolerable leakage, it is simply replaced

Valves:

Bypass Valve – internal to many pump heads that allow fluid to be recirculated if a given pressure limit is exceeded.

Check Valve – allows liquid to flow in one direction only. Generally used in discharge line to prevent reverse flow.

Foot Valve – a type of check valve with a built-in strainer. Used at point of liquid intake to retain liquid in system, preventing loss of prime when liquid source is lower than pump.

Relief Valve – used at the discharge of a positive displacement pump. An adjustable, spring-loaded valve opens when a preset pressure is reached. Used to prevent excessive pressure build-up that could damage the pump or motor.