Pressure/Vacuum Relief Valve,
Pilot-operated diaphragm valve

Función y Descripción

The PROTEGO® Type VN-A-PCPF pilot-controlled diaphragm valve is a newly developed valve for pressure and vacuum relief. Primarily used as a safety device for out-breathing in tanks, vessels, and process engineering equipment, it also offers reliable protection from overpressure and/or vacuum. It prevents the intake of air and excessive product vapor loss up to and until the set pressure is reached. 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 valve 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 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 reached. Once the valve has started to lift, it opens fully within a 10% pressure rise or the opening pressure difference, and the nominal volumetric flow is released through a fully open valve. If and when this level is exceeded, the pressure increase will follow the performance curve (∆p/V. curve). From set pressure to full capacity (fully open valve), the pressure increase is 100% in case of vacuum venting/in-breathing 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 possible through valve seats made of high-grade stainless steel with precisely lapped valve pallets. Once the excess pressure is relieved or the vacuum pressure has been balanced out, the valve reseats and seals tight again.

Características especiales y ventajas

  • controlled by corrosion-resistant control valve (pilot valve)
  • small amounts of tank substance is released into the atmosphere when the valve is opened
  • max. 10% pressure increase up to full lift
  • extreme tightness resulting in lowest possible product losses and reduced environmental pollution
  • set pressure close to opening pressure for optimum pressure maintenance in the system
  • protection of the main valve control diaphragm from low temperatures – high durability
  • high flow capacity
  • can be used in explosion hazardous areas
  • field test connection possible upon request
  • field test kit upon request

Basic design of pressure/vacuum relief valve with a control pilot valve


Basic design of pressure/vacuum relief valve with a control pilot valve


Additional special devices available upon request.

* It is recommended that an external control line is to be provided with direct connection to the tank.



+20 mbar +1034 mbar
+8 inch W.C. +415.1 inch W.C.


-2.0 mbar -7 mbar
-0.8 inch W.C. -2.8 inch W.C.
Higher or lower settings upon request

Diagrama de flujo volumétrico

Los diagramas de flujo volumétrico han sido determinados con un banco de pruebas de caudal calibrado y certifi - cado por TÜV. El flujo volumétrico V. en [m³/h] y el CFH se refi eren a las condiciones estándar de referencia de aire según ISO 6358 (20°C, 1bar). La conversión a otras densidades y temperaturas están referidas en el Vol. 1: “Fundamentos Técnicos”.