Air Bound – Sometimes called vapor lock, the eye of the impeller gathers air to a point where the pump is no longer able to generate pressure.

Atmospheric Pressure – The force exerted by atmosphere on the surface of the Earth. This force is equal to 14.7 psi at sea level and decreases as elevation rises. This is the condition that both allows and restricts suction lift in a pump.

Cavitation – A condition that arises when a pump is working to move more liquid than it can receive. This causes liquid in the volute to form small bubbles (vaporized liquid) that expand and contract. This process is damaging to the pump. Symptoms include loss of flow, vibration, noise, and damage to the pump. Cavitation is caused by over speeding the pump or operating at to high of a suction lift. It can typically be alleviated by slowing down the rpms of the pump.

Check Valve – A device that allows flow to travel in only one direction. An automatic priming type pump will have a check valve only on the discharge side of the volute where other types of pumps will have a check valve on the suction and the discharge. Sometimes these are called swing checks, gates, flapper, or foot valves.

Duty Point – The intersection of head and flow on a pump curve that gives expected performance.

Efficiency – The percentage of power that is converted into movement of the drive unit. In a pump there is the efficiency of the pump, how well does it convert power to movement of the liquid. It also relates to the efficiency of the pump drive system.

Best Efficiency Point (BEP) – The point on the curve where the pump operates at its highest efficiency. This point is typically in the middle of the curve.

Float Switches – Bulbs with internal mercury switches that allow a pump to start and stop depending on the level of liquid in the suction area.

Open Face Impeller – A set of vanes on a plate that rotate in a circular motion to move a liquid. Open face impellers tend to be less efficient but are able to handle a higher range of performance needs, handle larger solids, and obtain higher suction lift.

Closed Face Impeller – A set of vanes sandwiched between two plates that rotate in a circular motion to move a liquid. Closed faced or enclosed impellers are more efficient than open face impellers and thus produce more volume at a given horsepower than open face impellers. However, impellers are more susceptible to cavitation, wear, handle fewer solids, and have a lower suction lift capacity.

Net Positive Suction Head (NPSH) – This is the calculation, provided on a pump curve, that describes the amount of inlet pressure to avoid cavitation. By reading this curve, it is possible to estimate volumes at particular suction lifts.

Static Suction Lift – The vertical distance between the eye of the impeller and the surface of the liquid being pumped.

Static Discharge Head – The vertical distance between the eye of the impeller and the point of discharge.

Dynamic Discharge Head – The sum of the static discharge head and discharge friction loss.

Dynamic Suction Lift – The sum of the static suction lift and the friction loss in the suction line.

Total Dynamic Head (TDH) – The sum of the dynamic suction lift and dynamic discharge head.

Snore – The point at which the suction hose is not completely submerged. An efficient priming system is required to overcome the air introduced into the hose.

Water Hammer – Energy transmitted from the sudden stoppage in flow from the pump.