The positive displacement pump provides an approximate constant flow at fixed speed, despite changes in the counter pressure. Two main types of positive displacement pumps exist:

Rotary pumps

Reciprocating pumps

The flow from a centrifugal pump will change considerably. The flow of a rotary pump will change a little, while the flow of a reciprocating pump will hardly change at all.

The actual seal face surface is larger for rotary pumps than for reciprocating pumps. Even though the two pumps are designed with the same tolerances, the gap loss (fluid slippage) of the rotary pump is larger.  

These pumps are typically designed to the finest tolerances to obtain the highest possible efficiency and suction capability. However, in some cases, it is necessary to increase the tolerances, for example when the pumps have to handle highly viscous liquids, liquids containing particles or liquids of high temperature.  

A positive displacement pump makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe.

Pumps Expert distributes many different types of positive displacement pumps to suit a wide range of applications in building services, industry, petro-chemical, food and marine uses.

Considering the construction type, Positive Displacement pumps distributes by Pumps Expert are:

Reciprocating Pumps

Rotary Pumps