How Does Pressure Control Valve Work

11 January 2020

Basic mechanism of pressure control valve

 Image credit: CTE Skills

Every hydraulic system has an integrated pressure control valve. As the hydraulic pressure builds up, it may damage the system. Pressure control valves save your system from damage, wastage of power, and overheating.

There are different types of pressure control valves, and you should know how it works before choosing one. In this article we are going to explain the principles of control valve operation.

There are two categories of pressure control valves  -

  1. Direct Acting Valve
  2. Pilot Operated Valve

The Principle of Direct Acting Valve

A mechanical spring holds the flow of fluid in a direct acting valve. Here, the spring force and the hydraulic pressure work against each other in limiting the flow. Using the knob, you can change the tension in the spring which at a certain limit will result in the opening of the valve. The pressure at which the valve opens up is the cracking pressure. As you overcome the cracking pressure fluid will begin to pass through. At the full relief valve pressure, the valve is fully open permitting the maximum flow of liquid.

Direct Acting pressure control valve

 Image credit: Instrumentation Tools

The main parts of a pilot operated pressure control valves are a spring housing holding the control spring, an adjustable screw, pilot valve chamber, main valve chamber, and the main diaphragm chamber.

The Principle of Pilot Operated Valve

This screw is the primary control system maintaining the pressure. By tightening and loosening up the bolt, you can increase or decrease the output pressure respectively.

Pilot operated pressure control valve

 Image credit: ATO

At the start, the pressure adjusting bolt is kept entirely loose and steam begin to accumulate in the main valve chamber. Now if you tighten the main control screw at the top, it puts pressure on the adjustment spring. As a result, the pilot diaphragms deforms, and the pilot valve plungers push the SS valve which opens up the pilot valve.

As the pilot valve opens the pressurized steam in the main valve chamber enters the pilot valve chamber through the strainer screen. As steam build up in a controlled manner within the pilot chamber the main diaphragm deforms. The diaphragm pushes the push rod which opens up the main valve. As the main valve opens up the flow of steam is directed to the supply or downstream line. This line also has a feedback line which connects below the pilot diaphragms.

The feedback line is responsible for maintaining a balanced flow of steam. The balancing line provides upward pressure on the diaphragms. It balances the downwards force acting on the spring. Thus, the pilot valve throttles and controls how much steam passes to the pilot valve chamber. In response, the main valve passes the right amount of steam pressure necessary.

You can adjust the pressure coming out of the downstream line by controlling the adjustable bolt at the top. The whole system goes in a loop and balances itself automatically.

Pressure control valve types


Comparison between Direct Acting (DA) and Pilot Operated (PO) valves –

  • Cost: DA valves costs lower than PO
  • Size: DA valves are larger than PO valves of the same rating
  • Response time: DA valves have faster response time than PO
  • Designed for: DA are designed for lower pressure, whereas PO are designed for higher pressure

The principles of pressure control valve applies to many hydraulic systems that you might be operating. We hope this quick overview will help you get a better understanding of its importance and how it operates to safeguard your system.

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