Pressure Relief Valves Guide 101

In this blog post, you’ll read:Pressure Relief Valves (PRVs), often viewed as the last line of defense in many systems, play a pivotal role in ensuring the safety and stability of high-pressure systems. These vital components are more than just simple accessories; they're guardians of system integrity, protecting both equipment and operators from potential catastrophes. Let's delve deep into the world of PRVs.
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Industries use valves almost every day. Valves control, regulate, and shut off supplies. Plumbing valves are devices that carry out a lot of functions. They need to work correctly. Safety valves are the devices that save the system from overpressure. Relief valves are a type of safety valve. We use them to control increasing pressure.

Pressure Relief Valves (PRVs), often viewed as the last line of defense in many systems, play a pivotal role in ensuring the safety and stability of high-pressure systems. These vital components are more than just simple accessories; they’re guardians of system integrity, protecting both equipment and operators from potential catastrophes. Let’s delve deep into the world of PRVs.

A PRV is designed to release excessive pressure from a system when it exceeds a predetermined limit, preventing potential explosions or system failures. When the internal pressure reaches a certain threshold, the PRV activates, allowing fluids or gases to escape until the system returns to a safe pressure level.

What is a Relief Valve?

A pressure relief valve is a safety valve that controls pressure in a system. We need it when overpressure can cause problems. Pressure relief valves solve the problem of system failure due to pressure changes. A pressure relief valve is a critical safety device. It ensures the safe operation of pressurized systems. We must maintain and test these valves to ensure their proper functioning.

When the pressure in a system rises above a setpoint, the relief valve opens. It allows fluid to flow out of the system, which reduces the pressure to a safe level. The valve then closes once it relieves stress. The pressure relief valve must be set to open at a pressure below the setpoint. We should consider the pressure relief valve in case other control measures fail.

tankless water heater installation kits
Tankless water heater installation kits

How Does It Work?

The mechanism inside a PRV is ingeniously simple. When pressure inside a system increases beyond the set limit of the valve, the excessive force pushes against a sealing element (often a diaphragm or a spring-loaded piston). Once the pressure surpasses the resistance provided by the seal, the valve opens. As the excess is vented and pressure drops, the valve reseals itself.

What Are Raw Materials?

Pressure Relief Valves (PRVs) are essential safety devices in various systems, and the choice of raw materials plays a critical role in their function, durability, and compatibility with the medium they control. Let’s delve into the typical raw materials used in the construction of PRVs:

  1. Stainless Steel: This is one of the most common materials for PRVs, especially in applications where corrosion resistance is vital. Types 304 and 316 are frequently used due to their excellent resistance to various chemicals and high temperatures.
  2. Carbon Steel: A robust and cost-effective choice, carbon steel is used for PRVs in many standard applications. However, depending on the operating environment, they might require additional coatings or treatments to improve corrosion resistance.
  3. Bronze and Brass: These are commonly used for smaller PRVs, especially in plumbing applications. They offer good corrosion resistance, especially against water, but are less suited for aggressive chemicals or high-temperature scenarios.
  4. Cast Iron: Typically used in larger industrial PRVs, cast iron provides strength but can be susceptible to corrosion. As such, it’s often used in applications where the medium is not aggressive.
  5. Plastic and PVC: In specific applications, especially where corrosion from aggressive chemicals is a concern, PRVs made from plastics or PVC might be used. They are generally used in lower-pressure and temperature systems.
  6. Elastomers (Seals and Diaphragms): PRVs often contain elastomeric components like seals, gaskets, and diaphragms. Materials like nitrile, Viton, or silicone are chosen for compatibility with the system’s medium, temperature, and pressure conditions.
  7. Special Alloys: In some specialized applications, alloys like Monel, Hastelloy, or Inconel might be used, especially if the valve needs to handle extremely aggressive chemicals or very high temperatures.

The choice of raw material depends on various factors:

  • Medium Controlled: Whether the PRV is used for air, steam, water, oil, aggressive chemicals, or any other medium will significantly influence the material choice.
  • Operating Pressure and Temperature: Some materials can handle high pressures and temperatures better than others.
  • Corrosion Resistance: The material should resist any corrosive effects from the medium or the environment.
  • Cost and Availability: While some materials might be ideal from a performance perspective, they might be too expensive or not readily available.

It’s essential to ensure that the chosen material is compatible with the medium and operating conditions. Incorrect material selection can lead to PRV failure, posing risks to the system and its surroundings.

What are the sizes?

Pressure Relief Valves (PRVs) come in various sizes to accommodate multiple applications and system requirements. The size of a PRV is typically determined by the inlet and outlet diameter, often in inches or millimeters. The size is crucial as it dictates the flow rate the valve can handle when relieving excess pressure.

Common Sizes for Pressure Relief Valves include:

  • Small-Scale Applications: PRVs often range from 1/4 inch to 2 inches (6mm to 50mm) for residential or light commercial use, such as in water heaters or boilers. These sizes are suitable for most home appliances and small industrial equipment.
  • Medium to Large-Scale Industrial Applications: In larger industrial settings like refineries, chemical plants, and power stations, PRVs can range from 2 inches to 12 inches (50mm to 300mm) or even more extensive. The larger sizes are essential to handle the significant flow rates in these setups.
  • Specialized or Custom Applications: For specific applications, such as in the aerospace industry or unique manufacturing processes, custom-sized PRVs may be required. These can be smaller than 1/4 inch or larger than 12 inches, depending on the precise needs of the system.

It’s essential to select the correct size for a PRV. An undersized valve might not provide adequate relief during over-pressure conditions, putting the system at risk. Conversely, an oversized valve can be less efficient, more costly, and might not operate correctly if the system never reaches the valve’s intended activation pressure.

When choosing a size, it’s also important to consider other factors, such as:

  • Flow Rate Requirements: The volume of fluid or gas the valve must release during over-pressure conditions.
  • Set Pressure: The pressure at which the valve will open.
  • Backpressure: The pressure that might exist at the valve’s outlet can affect its operation.

Professional consultation and detailed system analysis are recommended to ensure the correct size and type of PRV is selected for any given application.


PRVs find their place in a plethora of applications:

  • Industrial Processes: Protecting equipment in chemical plants, refineries, and other industries where over-pressurization is a concern.
  • Home Appliances: Found in boilers and water heaters to prevent explosions due to pressure buildup.
  • Transportation: In automotive and aerospace industries, pressure systems, like hydraulic lines, operate safely.

Maintenance & Safety

While PRVs are designed to be reliable, regular checks are essential. A malfunctioning PRV can be catastrophic. Regular inspection and testing ensure the valve operates correctly, releasing at the designated pressure. Moreover, released fluids or gases should be safely channeled to avoid hazards.

Though small and often overlooked, Pressure Relief Valves carry the significant responsibility of ensuring safety in countless systems. Whether they’re safeguarding an industrial process or your home boiler, understanding their function and importance is crucial for anyone working around pressurized systems.

Product: Brass Pressure Relief Valve.
Material: CW617N, H58-3
Size: 1/2
Working Pressure: 1.3 Bar, 3 Bar, 6 Bar, 8 Bar
Thread Connection: BSP.
Applications: The applications include Water treatment plants and household uses.
Specs chart

Types of Pressure Relief Valves:

There are several types of pressure relief valves (PRVs) available. Each type has unique features and applications. Below are the kinds of Pressure Relief Valves.


1. Power Actuated Relief Valve: 

A power-actuated relief valve (PARV) is a type of pressure relief valve (PRV) that uses a power source. The source can be hydraulic fluid or compressed gas. It assists in opening the valve during overpressure conditions. The power actuator can be a piston or diaphragm. It helps in opening the valve during an overpressure event. A control system handles the actuator. It receives input from sensors that track the method.

When the system pressure rises above the set point, the actuator starts working; it opens the valve and relieves excess stress. The power actuator may also provide extra benefits. It includes faster response times and greater accuracy. They also can operate in high-pressure or high-temperature environments.

PARVs are common in applications where the system pressure is high. They are also applicable in the process, which requires a fast response time. Examples include power generation, chemical processing, and oil and gas production. We can also use them when a standard spring-loaded PRV is insufficient.

pressure safety valves with 1 mpa
pressure safety valves with 1 mpa

2. Temperature-Actuated Pressure Relief Valve:

A temperature-actuated pressure relief valve has a unique design to relieve excess pressure. The cause of stress may be the thermal expansion in pressurized systems. The valve works by using a temperature-sensitive element. The element can be a wax pellet or a bimetallic strip. It controls the opening and closing of the valve. When the temperature in the system rises above a set point, this element expands. It results at the beginning of the valve and relieves the excess pressure.

The main component of a temperature-actuated valve is a temperature-sensitive element. The temperature-sensitive part is present within the body. It responds to changes in the temperature of the system. The temperature-sensitive element contracts when the pressure in the system is relieved. The contraction closes the valve and prevents further fluid escape.

We use these valves in applications where thermal expansion may cause excessive pressure. It can be hot water heating systems or steam systems.

3. Spring-loaded Pressure Relief Valves:

inside parts of safety valve
Inside parts of the safety valve

These are the most common types of PRVs. They use a spring to hold a disk against a nozzle or seat. When the system pressure rises above the set pressure of the valve, the spring compresses. The disk lifts off the nozzle or seat. It allows fluid to escape and reduce tension. We use Spring-loaded PRVs in low-to-medium pressure applications.

4. Pilot-operated Pressure Relief Valves:

Pressure valve on medical supplies
Pressure valve on medical supplies

These valves use a pilot valve to control the opening and closing of the main valve. It uses a small amount of system pressure to operate the pilot valve. This pressure then holds the primary valve disk. Pilot-operated PRVs are applicable in high-pressure applications.

5. Safety Relief Valves:

 The design of the safety relief valve is to operate in steam application. It uses a spring-loaded disk to seal against a nozzle. When the pressure in the system rises above the set pressure of the valve, the disk lifts off the nozzle. It allows steam to escape and reduces stress. Safety relief valves are applicable in high-pressure steam applications.

6. Vacuum Pressure Relief Valves: 

A vacuum relief valve (VRV) protects pressurized systems from severe vacuum conditions. Vacuum conditions can occur when they expose an approach to a sudden drop in pressure. It may also happen when fluid drains from the system. These conditions create a vacuum that can cause the system to collapse or implode.

pressure reducing valve
pressure reducing valve

When the pressure in the system drops below atmospheric pressure, the spring compresses. It allows the seat to lift off the nozzle. The air enters the system as the disc moves away from the nozzle. It equalizes the pressure and prevents vacuum conditions from causing damage. Once the pressure in the system returns to normal, the spring pushes the seat, resealing the valve.

Vacuum valves are standard in applications where vacuum conditions may pose a risk. It includes storage tanks, pipelines, and other pressurized systems. We can also use them with different pressure relief valves for vacuum protection.

The choice of Pressure relief valve depends on the application. It is crucial to select the correct type of PRV. The valve should be set to the appropriate pressure. It ensures the safe and reliable operation of the system it protects.

Working Mechanism of Pressure Relief Valves:

The working mechanism of a pressure relief valve (PRV) is quite precise. The valve itself opens and releases excess pressure. It happens when the system pressure exceeds the “set pressure. The main components of a PRV include a valve body, a spring, a disk or seat, and a nozzle. The valve body houses the other features and provides a connection point to the system.

working mechanism of pressure relief valves
Working mechanism of pressure relief valves

The spring holds the disk against the nozzle. It creates a seal that prevents fluid from escaping under normal operating conditions. When the pressure in the system rises above the set pressure, it compresses the spring. It causes the disk to lift off the nozzle or outlet.

As the disk moves away from the nozzle, it escapes the fluid from the system. The process reduces the pressure back to the safe operating range. Once the pressure drops below the set point, the spring pushes the disk back onto the nozzle. It reseals the valve.

The pressure relief valve operates regularly to maintain the set pressure. It opens and closes as needed to prevent damage or injury. It is important to note that PRVs are critical safety devices. We must maintain them to ensure they are functioning well. They can provide reliable protection in the event of an overpressure situation.

Applications of Pressure Relief Valves: 

Here are some typical applications of pressure relief valves in various industries.

applications of pressure relief valves
Applications of pressure relief valves

Chemical Industry:

The chemical industry is one of the most significant users of pressure relief valves. PRVs protect reactors, tanks, and pipelines from overpressure conditions in this industry. We use these valves to protect equipment from overpressure. Causes of overpressure include blocked lines, excessive temperature, and chemical reactions. Pressure relief valves in the chemical industry handle corrosive and toxic chemicals. It requires unique materials to prevent degradation.

Oil and Gas Industry:

The oil and gas industry is another significant user of pressure relief valves. These valves protect oil and gas pipelines. They also serve protection in drilling operations. In offshore drilling operations, they are critical for preventing fatal blowouts. Such situations can lead to oil spills and other environmental disasters.

Petrochemical Industry:

The petrochemical industry has a close relation to the chemical industry. It also uses pressure relief valves to protect process equipment. Pressure relief valves protect equipment from overpressure due to temperature or chemical reactions. These industries also contain toxic chemicals. For this purpose, pressure relief valves have stable materials.

Pharmaceutical Industry:

The pharmaceutical industry is another industry that relies on pressure relief valves. Pressure Relief valves protect reactors and pipelines from overpressure conditions. These valves handle sensitive and delicate products that need strict quality measures.

Power Generation:

Power generation plants include nuclear power plants and thermal power plants. These industries have extensive use of relief valves. PRVs protect boilers, turbines, and critical parts from overpressure. They also protect pressure vessels and piping systems in steam distribution networks.

Water Treatment:

We also use Pressure relief valves in water treatment facilities. They handle water storage tanks, piping systems, and treatment plants by pressure control. They also protect water treatment plants from pressure during startup and shutdown.

Food Processing:

The food processing industry is another industry that uses pressure relief valves. They protect cookers and sterilizers from pressure. Pressure relief valves also protect pressure vessels and piping systems in these plants.

The applications of pressure relief valves are diverse. They range from chemical processing to food processing. Proper selection, installation, and maintenance of pressure relief valves are crucial. It ensures high performance and reliability in doing the job.

Hands of technician operating valve
Hands of the technician operating the valve

Advantages of Pressure Relief Valves: 

Pressure relief valves offer several benefits, including:

  • Protection From Overpressure:

 The top advantage of PRVs is their ability to protect the system from overpressure. Overpressure can cause system failure, damage, and even explosions. They have a self-mechanism to open and relieve excess pressure. It saves the system from damage to the system, personnel, or the environment.

  • Prevents Leaks:

 Relief valves can also prevent leaks in piping systems. They relieve pressure when it exceeds enormous working pressure. Leaks can be costly and can cause environmental damage. It can also cause threats to personnel.

  • Saves Energy: 

Relief valves can also help save energy by reducing the pressure when we don’t need it. It reduces the load on the system and results in lower energy consumption.

  • Extends Equipment Life: 

By preventing overpressure, these valves can help extend the life of the equipment. Overpressure can cause equipment fatigue, which can lead to decreased lifespan. Long life span makes it an economical choice.

  • Improves System Reliability: 

Pressure relief valves can help improve the reliability of a system. They prevent overpressure conditions that can cause downtime and maintenance issues. A reliable strategy can perform way better.

  • Compliance With Regulations: 

Many industries must follow the rules and standards that mandate using PRVs. It protects equipment and personnel from overpressure conditions. Following these regulations can prevent legal and financial consequences.

  • Versatility: 

Pressure relief valves are available in various types and sizes. They can fit different applications and systems. Their versatility makes them suitable for use in many industries and scenarios. It also makes pressure relief valves durable.

Drawing Of Safety Valve
Drawing Of Safety Valve


Pressure relief valves are the latest safety valves. They are adequate for protection purposes. We can use them in houses and every industry. They can save us from significant hazards of explosion. Pressure relief valves are excellent for maintaining secure systems. There are many materials available for these valves. Bronze relief valves, copper, brass, etc., are standard.

The material varies as per application. We can get a suitable relief valve by looking for the proper requirements. A buyer can prepare a buying guide before purchasing the product. It’s better to go through the maker’s product details. It helps tell one’s choices and priorities.

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