Pressure Sustaining or Back Pressure Regulating Valves regulate upstream pressures by relieving the surplus pressure downstream or via a return line (when installed in a tee). They work in much the same way as a relief valve (normally closed, opening at the set pressure) but are more accurate, responsive and only open far enough to relieve sufficient pressure to maintain the desired pressure upstream. The pressure to be maintained is known as the set pressure and is easily adjusted by turning the adjusting bolt, thus compressing the spring (clockwise increases the set pressure, anti-clockwise reduces the set pressure).
There are some general rules to help select the best regulator and the best control for each application:-
• Unlike other valves where the valve size matches the pipe size, these pressure control valves must be “sized”, using the differential between upstream/downstream pressures and considering whether the valve has to bypass a small percentage of the flow or the whole output of the pump. For this reason it is not unusual to select a valve that is different to the pipe size.
• Self acting valves are the simplest design and represent the lowest cost but they are not as accurate as pilot operated valves.
• Always use the lightest spring (smallest range that covers the set pressure)
• Where high pressures occur upstream and there is minimal back pressure downstream, the high differential pressure may cause cavitation. Some of the effects of cavitation can be excessive noise, premature wear of valve or other components in the downstream piping. A simple remedy is to create some back pressure (e.g. install a globe valve, partially closed) in the downstream piping.
The following range is extensive, mainly because every regulator has limitations on sizes, materials of construction, suitability to various media, inlet pressures and reduced pressure ranges. In addition to the metal bodied valves offered we have quality thermoplastic sustaining valves (DHV716/725) as well.
