Pressure – Reducing valves and its Applications

Pressure reducing valve is a type of pressure control valve. This type of valve is used to maintain constant reduced pressure in a pipeline where the flow is fluctuating. This type of valve (which is normally open) is used to maintain reduced pressures in specified locations of hydraulic systems. The high incoming pressure is reduced to a constant pressure level to protect the important instrument.

Construction & Working:


The principal parts of the reducing valve are the main valve; an upward-seating valve that has a piston on top of its valve stem, an upward-seating auxiliary (or controlling) valve, a controlling diaphragm, and an adjusting spring and screw.

A pressure-reducing valve uses a spring-loaded spool to control the downstream pressure. If the downstream pressure is below the valve setting, the fluid flows freely from the inlet to the outlet.

Reducing valve operation is controlled by high pressure at the valve inlet and the adjusting screw on top of the valve assembly. The pressure entering the main valve assists the main valve spring in keeping the reducing valve closed by pushing upward on the main valve disk

However, some of the high pressure is bled to an auxiliary valve on top of the main valve. The auxiliary valve controls the admission of high pressure to the piston on top of the main valve. The piston has a larger surface area than the main valve disk, resulting in a net downward force to open the main valve. The auxiliary valve is controlled by a controlling diaphragm located directly over the auxiliary valve.

The controlling diaphragm transmits a downward force that tends to open the auxiliary valve. The downward force is exerted by the adjusting spring, which is controlled by the adjusting screw. Reduced pressure from the main valve outlet is bled back to a chamber beneath the diaphragm to counteract the downward force of the adjusting spring.



  • Air compressor
  • Aircraft and aerospace
  • Oxyfuel welding and cutting
  • Used in inlet flow of load in pressure reactor
  • Mining industries



Instrumentation Engineer

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