A DPCV contains a diaphragm that separates the upper / lower chambers of the valve and a spring-loaded piston. The piston is connected to the diaphragm, and closes the valve when differential pressure rises and opens it as the differential pressure falls. For those periods of equilibrium between diaphragm pressure and the piston spring, the valve position remains steady.
DPCVs are important to the efficient operation of systems based on variable speed pumps and 2-port control valves.
In variable flow circuits, Differential Pressure Control Valves (DPCV) are typically used to maintain a constant pressure differential across a sub-branch. This protects downstream control valves from excessive pressures, and also neutralises the effects of pressure variation caused by other control valves in the circuit.
Once a sub-branch has been commissioned, the DPCV prevents interference from other parts of the system. This makes the commissioning process much easier. As DPCVs can be set to maintain a specified pressure differential or flow rate, there is generally no need to include regulating valves at the same location. However, test points adjacent to DPCVs are recommended for ease of commissioning and future fault-finding.