Positive displacement pump

It is not mandatory to install a check valve at the outlet of positive displacement pumps. However, the flow rate of these pumps changes very little with pressure; contrary to the trend in centrifugal pumps where the shaft power decreases as the head increases, the shaft power of positive displacement pumps increases as pressure rises. This requires the installation of safety valves on the positive displacement pump and within the pumping system, to prevent accidental blockages in the discharge pipeline that could lead to excessive pump pressure, thereby resulting in high power consumption and damaging the prime mover or the pump due to overload. Therefore, the outlet valve must not be closed when starting the positive displacement pump. Positive displacement pumps draw in and discharge liquid by causing the working volume to periodically increase and decrease due to the movement of the working components, and directly increase the pressure energy of the liquid through the compression exerted by these components. 　　Based on the way their moving parts move, positive displacement pumps are divided into two categories: reciprocating pumps and rotary pumps. 　　Depending on the structure of their moving parts, positive displacement pumps are further divided into piston pumps and plunger pumps, as well as gear pumps, screw pumps, vane pumps, and water ring pumps.

Logically, there is no need to install a check valve at the outlet of a positive displacement pump, as the outlet of such a pump already functions like a check valve

A check valve is not required at the outlet of a positive displacement pump, but a safety valve must be installed. The positive displacement pumps commonly used on-site include gear pumps, metering pumps, peristaltic pumps, vane pumps, etc