Pump Terminology


Best Efficiency Point (B.E.P.): The point on a pump's performance curve at which it is most efficient.


Casing: The body of the pump which encloses and protects the impeller and other internal pump components.

Cavitation: The sudden collapse of gas bubbles in a pump due to the sudden pressure increase. This can occur if the pressure in a pump chamber is lowered below the vapor pressure of the liquid.

Centrifugal force: A force generated by a rotating body that extends outward from its center. In the case of a centrifugal pump, this force is imparted on the fluid by rotating impeller blades.


Equipment: Refers to any device in the system other than pipes, pipe fittings and isolation valves.


Friction: The force produced between two surfaces in resistance to movement. All fluids produce friction when they are in motion. The higher the fluid viscosity, the higher the friction force for the same flow rate. Friction is produced internally as one layer of fluid moves with respect to another and also at the fluid/wall interface.


Head: Refers to the pressure produced by a vertical column of fluid. As a pump specification, it denotes the height above the suction inlet that a pump can lift a fluid. It defines the mechanical energy of the flow per unit weight.


Impeller: the rotating element of a pump which imparts movement and pressure to a fluid via centrifugal force.


Laminar: A distinct flow regime that occurs at low Reynolds number (Re < 2000). It is characterized by particles in successive layers moving past one another in a well behaved manner.


Net Positive Suction Head (N.P.S.H.): The head in feet of water absolute as measured or calculated at the pump suction inlet, minus the vapor pressure (converted to feet of water absolute) of the fluid


Operating point: The point at which the system curve and pump performance curve intersect in order to meet the flow and head process requirements.


Performance curve: A curve of flow vs. Total Head for a specific pump model and impeller diameter.

Pipe roughness: A measurement of the average height of peaks producing roughness on the internal surface of pipes. Roughness is measured in many locations, and is usually defined in micro-inches RMS (root mean square).

Pressure: The application of external or internal forces to a body producing tension or compression within the body. This tension divided by a surface is called pressure.


Shut-off head: The total head corresponding to zero flow on the pump performance curve.

Specific gravity: The ratio of the density of a fluid to that of water at standard conditions.

Siphon: A system of piping or tubing where the exit point is lower than the entry point.

System: A system in the context of pumping refers to all the piping (with or without a pump) starting at the inlet point (often the fluid surface of the suction tank) and ending at the outlet point (often the fluid surface of the discharge tank).

System curve : Is a plot of flow vs. total head that satisfies the system requirements.

System equation: The equation for total head vs. flow for a specific system. This equation incorporates friction and system inlet and outlet conditions (i.e. velocity, elevation and pressure).


Total dynamic head (TDH): A term identical to total head. This term is no longer used and has been replaced by the shorter total head.

Total Head(TH): The difference between the head at the discharge and suction inlet of the pump.

Turbulent: A type of flow regime characterized by the rapid movement of fluid particles in many directions as well as the general direction of the overall fluid flow.


Vapor pressure: The pressure at which molecules enter the vapor phase (i.e. when a liquid boils) at a specified temperature.

Viscosity: A property which measures a fluid's resistance to movement. The resistance is caused by internal friction in the fluid.


Work: The energy required to drive the fluid through the system.