VN-A-PC

Pressure/Vacuum Relief Valve, Pilot-operated diaphragm valve

Function and Description

The PROTEGO® Type VN-A-PC pilot-controlled diaphragm valve is a newly 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 overpressure and/or vacuum. It prevents intake of air and unacceptable product vapor loss up to and until the set pressure is reached. In the valve can be used as an inbreathing device. In such applications, the main valve is directly controlled when exposed to a vacuum, i.e. it functions as a weight-loaded diaphragm valve.

The main valve is actuated by a pilot valve, which is controlled by the tank pressure. A small amount of vapor is released into the atmosphere by the pilot when the valve opens. The set pressure is adjusted by increasing or decreasing the tension on the spring on the pilot valve.

As the pressure increases, the closing force acting on the main valve pallet increases, i.e. the valve seat to valve pallet seal becomes tighter with increasing tank pressure until the set pressure is reacted. Once the valve has commenced to lift 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 pressure, with seal-tight requirements far above common standards. This feature is achieved through valve seats made of high-grade stainless steel with precisely lapped valve pallets. Once the excess pressure is relieved or pressure below atmospheric balanced out, the valve reseats and seals tight again.

Features and Advantages

• corrosion-resistant pilot valve
• small amounts of fluid released into the atmosphere by the pilot when the main valve opens
• full lift at less than 10% overpressure
• extremely tight seal, minimal product loss, low environmental impact, reduced explosion risk
• set pressure close to the opening pressure resulting in best possible pressure management of the system
• control diaphragm of the main valve shielded from low temperatures - long service life
• very high flow capacity
• suitable for use in hazardous areas
• Field-Test-Connection upon request
• Field-Test-Kit upon request

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