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Operating Principle

Rotary Animation

The Basic Operating Principle

A Positive Displacement Pump has an expanding cavity on the suction side of the pump and a decreasing cavity on the discharge side. Liquid is allowed to flow into the pump as the cavity on the suction side expands and the liquid is forced out of the discharge as the cavity collapses. This principle applies to all types of Positive Displacement Pumps whether the pump is a rotary lobe, gear within a gear, piston, diaphragm, screw, progressing cavity, etc. 

Example: Rotary Lobe Pump

A relief valve on the discharge side of a Positive Displacement Pump is an absolute must - no ifs, ands or buts about it!

Internal Pump Relief Valves

Pump manufacturers normally have an option to supply an internal relief valve. These relief valves will temporarily relieve the pressure on the discharge side of a pump operating against a closed valve. They are normally not full ported, i.e. cannot by pass all the flow produced by the pump. These internal relief valves should be used for pump protection against a temporary closing of a valve.

External Relief Valve

An external relief valve(RV) installed in the discharge line with a return line back to the supply tank is highly recommended to provide complete protection against an unexpected over pressure situation.


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