Pressure/Vacuum Relief Valve
Pilot-operated diaphragm valve
Function and Description
The PROTEGO® Type PM-HF pilot-controlled diaphragm valve is a highly developed valve for pressure and vacuum relief. Primarily used as a safety device for outbreathing in tanks, vessels, and process engineering equipment it also offers reliable protection from vacuum and overpressure. It prevents intake of air and unacceptable product vapor loss up to and until the set-to- operate pressure is reached. The valve can be used as an inbreathing device as well. In such an application, the main valveis directly controlled when exposed to a vacuum, i.e. it functions as a weight-loaded diaphragm valve.
The main valve is controlled by a pilot valve. The latter in turn is controlled by the tank pressure. A small amount fluid stored in the tank released into the atmosphere by the pilot when the valve opens. The set-to-operate pressure is adjusted on the pilot valve by increasing or decreasing (as appropriate) the tension of a spring.
As the working pressure rises, the closing force acting on the main valve increases, i.e. the valve's tight-sealing is enhanced until the set-to-operate pressure is reached, thus preventing leakage. Once the valve has commenced to lift it opens fully within a 10% pressure rise or the opening pressure difference and the nominal volumetric flow is discharged through a fully open valve. If and when this level is exceeded the pressure increase will follow the performance curve (Δp/V.curve). From set pressure to full capacity (fully open valve) the pressure increase is 100% in case of vacuum venting/inbreathing function.Due to the sophisticated manufacturing technology, the tank pressure is maintained up to the set-to-operate pressure, with seal-tight requirements far above common standards being met. This feature is achieved through valve seats made of high-grade stainless steel with precisely ground valve pallets. Once the excess pressure is relieved or pressure below atmospheric balanced out, the valve reseats and seals tight again.
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