Glossary of Pump Terms

09/08/2016
Glossary of Pump Terms

Have you ever wondered what we meant when we talk about flow, head or viscosity? Perhaps you’ve wondered what the difference was between a centrifugal pump and a positive displacement pump or maybe you’re struggling to remember what B.E.P. stands for?

Bookmark this page and never be stumped again as we feature 25 common pump terms and their meanings.

 

1. Pressure

The back-pressure on the pump discharge caused by the head or another restriction.

 

2. Centrifugal Pump

One which transfers energy to the liquid by means of an impeller; ie. “a rotating device equipped with suitable vanes”. (The liquid is therefore delivered in a continuous and uninterrupted flow).

 

3. Positive Displacement Pump

One which transfers energy to a liquid by means of a reciprocating piston, or similar device, giving an intermittent or pulsed flow.

 

4. Ejector or Jet Pump

By mixing a high speed drive medium with a low velocity pumped medium, an energy exchange is achieved converting velocity energy into pressure, giving a continuous flow.

 

5. Static Head

The head against which the pump must work when the liquid is stationary.

 

6. Friction Loss Head

The head generated by friction of moving liquid, against the walls of the discharge pipes.

 

7. Net Positive Suction Head (npsh)

Energy from an outside source ie, static head or atmosphere pressure required to ensure liquid enters the pump volute.

 

8. Cavitation

Cavitation occurs when there is insufficient npsh ie, too low a suction pressure induces cavitation. This causes erosion to the metal surfaces due to the vapour bubble collapsing, allowing the liquid to rush into the subsequent spaces at high velocity, thus creating a water hammer effect.

 

9. 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.

 

10. Flow

The measurement of the liquid volume capacity of a pump. Often given in litres per minute (L/min), litres per second (L/sec) and metres3 an hour (m3/hr).

 

11. Performance Curve

A graph depicting the plot of total head vs flow rate for a specific pump, with a specific impeller and set of characteristics.

 

12. Pipe Friction Loss

The loss in head due to the friction between the process fluid and the walls of the pipes and joints.

 

13. 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.

 

14. Total Head

The sum of the head produced by the pump. It can be calculated by subtracting the suction head from the discharge head. Also referred to as Total Dynamic Head.

 

15. Pressure

Is the ratio of a force over an area over which the force is applied. Often measured in psi or kpa.

 

16. Pressure Drop

The difference in pressure between two areas of a pump, or between the inside and outside of a container.

 

17. Efficiency

The measured power out of a piece of equipment divided by the power produced by the piece of equipment. Shown as a percentage.

 

18. 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 the volumetric flow rate of the pump for which the pump was designed to convert the most kinetic energy into pressure energy.

 

19. 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.

 

20. 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.

 

21. Specific Gravity (SG)

The ratio of the density of a substance compared to the density of a reference (usually water at 4°C).

 

22. Viscosity

Resistance to gradual deformation of a fluid by shear or tensile stress.

 

23. Flooded Suction

If the pump is below the liquid source, and the suction is fed by gravity. This is a preferred method for centrifugal pumps.

 

24. 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.

 

25. Suction Static Lift

Only occurs when the pump is above the inlet reservoir.