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Relief / Suastaining

   Hydraulic control valve.pdf


The pilot of Relief / Sustaining valve is a normally closed type. It remains closed and thereby not allowing fluid from main valve bonnet chamber to leak out. This causes main valve to remain closed drip tight. When upstream pressure exceeds preset value, the pilot “leaks” off fluid from main valve’s bonnet chamber hereby allowing main valve to open. In turn, this allows fluid from pipeline to flow through. The “relief” effect is therefore realized. Both Pressure Relief & Pressure Sustaining valves have exactly the same configuration. When the valve is installed with downstream side to act as “relief” like purging fluid off into atmosphere or back into suction tank, it is known as “Relief Valve”.
However, when the main valve is installed in a pipeline whereby it functions to ensure that the upstream maintains a certain preset pressure, this is known as “Pressure Sustaining Valve”.

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