Its purpose is to achieve higher vacuum (lower pressure) than is possible by use of positive displacement pumps alone.

Values of specific speed less than 500 are associated with positive displacement pumps.

An alternative type of positive displacement pump should then be considered.

This type of circuit can use inexpensive, constant displacement pumps.

A relief or safety valve on the discharge side of the positive displacement pump is therefore necessary.

A peristaltic pump is a type of positive displacement pump.

A practical difference between dynamic and positive displacement pumps is how they operate under closed valve conditions.

Positive displacement pumps are the most effective for low vacuums.

In this configuration the positive displacement pump serves two purposes.

This is the principle behind positive displacement pumps, like the manual water pump for example.