Boasting a reputation for producing high quality, durable products, our collection of Pressure Relief Valves are guaranteed to provide effective and reliable pressure relief.

While some basic components and activations in relieving pressure may differ between the specific types of relief valves, each aims to be 100% effective in keeping your equipment running safely. Our current range includes numerous valve types, from flanged to spring-loaded, threaded to wireless, pilot operated, and much more.  

Air Pressure Relief Valves: Purpose & Functionality

A pressure relief valve is a type of safety valve designed to control the pressure in a vessel. It protects the system and keeps the people operating the device safely in an overpressure event or equipment failure.  

How does a pressure relief valve work?

A pressure relief valve is designed to withstand a maximum allowable working pressure (MAWP). Once an overpressure event occurs in the system, the pressure relief valve detects pressure beyond its design's specified capability. The pressure relief valve would then discharge the pressurized fluid or gas to flow from an auxiliary passage out of the system.  

Below is an example of one of our pilot operated pressure relief valves in action; the cutaway demonstrates when high pressure is released from the system.  

Farris 3880 Pilot Operated Pressure Relief Valve:


Pressure Relief Valve Applications

Air pressure relief valves can be applied to a variety of environments and equipment. Pressure relief valves are a safety valve used to keep equipment and the operators safe too. They're instrumental in applications where proper pressure levels are vital for correct and safe operation. Such as oil and gas, power generation like central heating systems, and multi-phase applications in refining and chemical processing. 

Types of PRVs

At Curtiss-Wright, we provide a range of different pressure relief valves based on two primary operations – spring-loaded and pilot operated. Spring-loaded valves can either be conventional spring-loaded or balanced spring-loaded.

Spring-loaded PRVs

Spring-loaded valves are programmed to open and close via a spring mechanism. They open when the pressure reaches an unacceptable level to release the material inside the vessel. It closes automatically when the pressure is released, and it returns to an average operating level. Spring-loaded safety valves rely on the closing force applied by a spring onto the main seating area. They can also be controlled in numerous ways, such as a remote, control panel, and computer program.   


  • Operate at higher set pressures than pilot-operated relief valves
  • Extensive range of chemical compatibility
  • Operate at high temperatures


Pilot-operated Pressure Relief Valves

Pilot-operated relief valves operate by combining the primary relieving device (main valve) with self-actuated auxiliary pressure relief valves, also known as the pilot control. This pilot control dictates the opening and closing of the main valve and responds to system pressure. System pressure is fed from the inlet into and through the pilot control and ultimately into the main valve's dome. In normal operating conditions, system pressure will prevent the main valve from opening.  
The valves allow media to flow from an auxiliary passage and out of the system once absolute pressure is reached, whether it is a maximum or minimum level.  
When the pressure is below the maximum amount, the pressure differential is slightly positive on the piston's dome size, which keeps the main valve in the closed position. When system pressure rises and reaches the set point, the pilot will cut off flow to the dome, causing depressurization in the piston's dome side. The pressure differential has reversed, and the piston will rise, opening the main valve, relieving pressure.  
When the process pressure decreases to a specific pressure, the pilot closes, the dome is repressurized, and the main valve closes. The main difference between spring-loaded PRVs and pilot-operated is that a pilot-operated safety valve uses pressure to keep the valve closed.  
Pilot-operated relief valves are controlled by hand and are typically opened often through a wheel or similar component. The user opens the valve when the gauge signifies that the system pressure is at an unsafe level; once the valve has opened and the pressure has been released, the operator can shut it by hand again.  

Pilot Operated Valve Advantages: 

  • Modulating control PORVs minimize the release of media 
  • Increasing pressure helps to maintain the pilot's seal. Once the setpoint has been reached, the valve opens. This reduces leakage and fugitive emissions.  
  • Smaller design than spring-loaded valves and larger pipe sizes 
  • Operate at pressures very close to the setpoint 
  • PORVs are unaffected by back pressure 
  • PORVs with remote sensing options are cost-effective solutions for PRV installations experiencing inlet pressure loss 
  • More options for control  
  • Can be used in engines 
  • Seals more tightly as the system pressure approaches 

Pilot Operated Valve Disadvantages: 

  • More complex 
  • More expensive at smaller sizes 
  • Small parts in pilot valve are sensitive to contaminant particles. 
  • Soft goods typically installed in pilot valves cannot withstand higher temperature fluids. 

Pilot Operated Valve Functioning Mode 

There are two functioning modes: 

Snap acting 

At set pressure the valve snaps to full lift. This can be quite violent on large pipes with significant pressure. The pressure has to drop below the set pressure in order for the piston to reseat. 


The pilot is designed to open gradually, so that less of the system fluid is lost during each relief event. The piston lifts in proportion to the overpressure. 



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How often should I test air pressure relief valves? Arrow

Pressure relief valves should be subject to an annual test, one per year. The operator is responsible for carrying out the test, which should be done using an air compressor. It’s imperative to ensure pressure relief valves maintain their effectiveness over time and are checked for signs of corrosion and loss of functionality. Air pressure relief valves should also be checked before their installation, after each fire event, and regularly as decided by the operators.  

What causes an overpressure event? Arrow

There are many causes of overpressure, but the most common ones are typically blocked discharge in the system, gas blowby, and fire. Even proper inspection and maintenance will not eliminate the occurrence of leakages. An air pressure relief valve is the only way to ensure a safe environment for the device, its surroundings, and operators.   

What is a pilot operated valve? Arrow

A pilot operated valve is an emergency relief valve that functions during an overpressure event.  

What is the difference between pilot-operated and direct operated? Arrow

Direct-acting solenoid valves have a direct connection with the opening and closing armature, whereas pilot-operated valves use of the process fluid to assist in piloting the operation of the valve. 

What’s the difference between a prv and psv? Arrow

A PRV and PSV are interchangeable, but there is a difference between the two valves. A pressure release valve gradually opens when experiencing pressure, whereas a pressure safety valve opens suddenly when the pressure hits a certain level of over pressurization. Safety valves can be used manually and are typically used for a permanent shutdown. Air pressure relief valves are used for operational requirements, and they gently release the pressure before it hits the maximum high-pressure point and circulates it back into the system.  

Control Valve Monitoring

How does a control valve work? Arrow

A control valve works by varying the rate of fluid passing through the valve itself. As the valve stem moves, it alters the size of the passage and increases, decreases or holds steady the flow. The opening and closing of the valve is altered whenever the controlled process parameter does not reach the set point.   

What are the three types of industrial relief valves? Arrow

The three basic types of industrial relief valves are conventional spring loaded, balanced spring loaded, and pilot operated.   

What is PSV in industry? Arrow

A PRV is often referred to as a pressure relief valve, which is also known as a PSV or pressure safety valve. They are used interchangeably throughout the industry depending on company standards. 

What is the purpose of a relief valve? Arrow

An industrial relief valve is designed to control or limit surges of pressure in a system, most often in fluid or compressed air system valves. It does so as a form of protection for the system and defending against instrument or equipment failure. They are usually present in clean water industries.  

Where is a control valve located? Arrow

Control valves are usually at floor level or easily accessible via platforms. They are also located on the same equipment or pipeline as the measurement and downstream or flow measurements.  

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