The valve is installed in the bypass between the flow and return pipes and opens on rising differental pressure to allow flow through the bypass.
This maintains the differential pressure between the flow and return
pipes at the predetermined set value. Differential bypass valves are used in systems with variable flowrates. Radiator circuits utilising thermostatic radiator valves or heating systems incorporating 2-port control valves are typical applications.
Differential bypass valves can be used in both constant and variable
volume systems to prevent the differential pressure from rising, which can seriously affect the performance of the 2-port control valves.
The 519 differential bypass valves use a stainless steel compression
spring to exert a pre-determined force onto the disc. The force is adjustable by turning the control knob to set the required differential pressure between 1 to 6 m head which corresponds to 10 to 60 kPa. The setting is then locked using the locking screw on the side of
the control knob to prevent unauthorised adjustment.