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What is Pressure Relief Valve

A pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system. It is designed to automatically release pressure when it exceeds a predetermined level, preventing potential damage or catastrophic failure. When the pressure reaches the set limit, the valve opens, and fluid or gas is released to a safe location, such as the atmosphere or a containment system.

Benefits of Pressure Relief Valve

Timely protection of safety
When the pressure in the system is too high and is not released in time, it may cause equipment and pipeline ruptures and cause accidents. The pressure relief valve can prevent the system from over-pressurization, thereby protecting the safety of equipment and personnel. ‌

Simple design and easy maintenance
Compared with other safety devices, the pressure relief valve is very simple in design and easy to maintain and replace. ‌As a mechanical device, the pressure relief valve can operate for many years without replacement or worrying about failure. ‌

Prevent oil tank deformation or bursting
When an accident occurs inside the oil-immersed electrical equipment, the oil in the oil tank is gasified and produces a large amount of gas, which causes the internal pressure of the oil tank to rise sharply. The pressure relief valve can open and release the pressure in time to avoid deformation or even bursting of the oil tank. ‌

Less leakage, reliable operation
As a transformer fault pressure protection device, the pressure relief valve has less leakage, reliable operation and reusability compared to old overpressure protection devices such as safety airway and explosion-proof membrane.

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How Pressure Relief Valves Work

A pressure relief valve is a direct-acting device, which means pressure acts directly upon the internal components of the valve. Pressure relief valves are normally closed, with internal components held in a position that creates a seal to prevent flow. When pressure increases beyond the valve’s specified limit, the valve is forced open, allowing fluid to vent out of the pressurized area to another section of the system or into the surrounding environment. By allowing fluid to vent, the pressure relief valve prevents pressure from increasing further and/or reduces the pressure within the system. After the pressure reduces to an acceptable level, the valve will return to its normally closed position and will shut off flow.

Differences Between Pressure Relief Valves and Safety Valves

Pressure relief valves have a continuous, proportional operation, whereas safety valves do not . Pressure relief valves are an operational part of fluid systems rather than only a safety feature. During normal operation, it's normal to have a continuously opened overflow/pressure relief valve to help the system rebalance to normal working conditions.

Safety valves, on the other hand, must remove all energy that may enter a system to prevent system failure. After the initial lifting of the disc, the area on which pressure acts enlarges, and the force on the spring increases significantly. The significant force causes the safety valve's popping characteristic.

A pressure relief valve’s blowdown is much narrower than a safety valve’s. This means there is a much smaller difference between the set pressure and closing pressure, meaning it closes faster.

How Does a Pressure Relief Valve Control or Limit Pressure in a System?

A pressure relief valve does not control or limit pressure in a system; instead, it is a safety device that prevents pressure from exceeding a predetermined level. In other words, a pressure relief valve is a reactive device that responds to an over pressure situation and prevents further pressure buildup. The valve is typically set to open at a specific pressure level, known as the set point or blow-off pressure, and is designed to release fluid or gas from the system until the pressure drops below this set point.

Pressure relief valve are typically installed with other pressure control devices, such as pressure regulators or control valves, that actively control and maintain the pressure within a desired range. Together, these devices help ensure pressure systems’ safe and reliable operation.

Types of Pressure Relief Valve

Hydronic Pressure Relief Valves
Hydronic pressure relief valves are a series of varied pressure relief valves used for hydronic applications. These applications involve hydronic systems, which transfer hot water through various machines and appliances. Hydronic systems take the outlet forms of radiators, baseboards, radiant tubing and heating devices like boilers and forced air systems.

Water Pressure Relief Valves
Water pressure relief valves are often used by private and municipal water supply companies. These machines are used in pumps for a variety of different reasons including—but not limited to—firefighting, high-rise buildings, water towers, drinking water applications and water tanks. Water pressure reducing valves work with the devices above and remove excess pressure by opening up, thereby minimizing the pressure.

Back Pressure Valves
Back pressure valves are pressure regulator valves used in pipes and pumps. They are essential in the plumbing industry. Their function is to maintain a set pressure, particularly at the pump’s outlet port or discharge, and doing so ensures correct metering.

How to Choose The Right Pressure Relief Valve

Valve materials

Pressure relief valves come in different metals. Each metal is meant to cater to specific applications. Depending on the system, a valve made with a certain material may be needed to ensure safety and proper operation. For example, stainless steel pressure relief valves have properties that allow them to work best in plants with corrosive materials.

Connection size and type

Just as each pressure relief valve is made with a variety of metals, each valve also features a specific design with a distinct connection size and type. The size of the valve must be at least as big as the inlet and discharge piping. In addition, certain valves are designed for specific connector types.

Set pressure

Pressure relief valve are designed to withstand great amounts of pressure and high temperatures, but each device has its own specific limits. The set pressure is the pressure that causes the valve to open, and it’s measured in pounds per square inch (PSIG).

Back pressure

Back pressure, or the pressure on the outlet side of the valve from the discharge system, will also contribute to the maximum allowable working pressure of the valve. This factor can be constant or variable to the plant’s operation. Constant back pressure will require a pilot-operated valve. Variable valve pressure cannot exceed 10% of the valve set pressure.

Temperature

Pressure relief valves can also withstand high temperatures. However, specific metals can only handle certain temperatures. So the temperature of the system needs to be taken into account to ensure proper valve selection.

Required capacity

While pressure relief valves can alleviate a great amount of pressure, they do have their limits. The maximum capacity of pressure they can relieve depends on multiple aspects, including the design of the valve and the temperature of the liquid or gas flowing through them. Having the right pressure relief valve will not only ensure smooth operations but also the necessary protection and safety a plant needs.

Pressure Relief Valve Testing Methods

Bench Testing
The most commonly mandated form of pressure relief valve testing, bench testing is unique in that it requires you completely shut down your facility’s system and remove all pressure relief valves. The valves are then transported to a lab where they are tested and repaired as necessary. Tested valves are then re-installed in your system.

Inline Testing
Inline testing is another accurate pressure relief valve testing method that doesn’t require the removal of valves or facility downtime. With inline safety relief valve testing equipment, a trained technician can test valves in the system to calculate the real setpoint of a valve in the system.

Operated in Place
Some pressure relief valve testing requirements will call for regular manual testing for freedom of operation. This is a basic test that can be done on-site. To complete an operated-in-place test, the test lever on the valve is manually activated. This test functions to ensure that the valve can open and shut tightly, but it does not verify at what pressure the valve opens and shuts. This is a test that may be required quarterly or bi-annually, to ensure the most basic functionality of safety relief valves.

Application of Pressure Relief Valve

Industrial machinery

Pressure relief valves are used in industrial machinery to protect equipment from overpressure conditions that could cause mechanical failure or accidents. They ensure safe operation by releasing excess pressure in systems such as hydraulic presses, boilers, and compressors.

Oil and gas industry

In the oil and gas industry, pressure relief valves are essential for protecting pipelines, storage tanks, and processing equipment from overpressure situations. They help prevent explosions, leaks, and equipment damage, ensuring the safety and efficiency of operations.

Chemical processing plants

Chemical processing plants use pressure relief valves to control pressure in reactors, storage vessels, and piping systems. These valves prevent overpressure that could lead to hazardous chemical releases, equipment damage, or catastrophic failures.

Water and wastewater treatment

In water and wastewater treatment facilities, pressure relief valves are used to manage pressure in pumps, pipes, and filtration systems. They protect the infrastructure from damage due to pressure spikes and ensure the smooth operation of treatment processes.

Fire protection systems

Pressure relief valves are critical components in fire protection systems, such as sprinkler systems and fire hydrants. They regulate pressure to prevent damage to the system and ensure adequate water flow and pressure during fire emergencies, enhancing the effectiveness of firefighting efforts.

Components of Pressure Relief Valve

Body

The main casing that houses the internal components of the pressure relief valve. It is typically made from durable materials such as brass, stainless steel, or cast iron to withstand high pressure.

Poppet or disc

A moveable component that seals against the valve seat to prevent fluid flow when the system pressure is below the set limit.

Valve seat

The surface against which the poppet or disc seals to prevent fluid flow under normal operating conditions. It is designed to create a tight seal to ensure accurate pressure control.

Spring

The tension of the spring determines the pressure at which the valve will open, and it can be adjusted to set the desired relief pressure.

Diaphragm or piston

Some pressure relief valves use a diaphragm or piston to sense the system pressure and actuate the poppet or disc.

Bonnet

The top cover of the valve body that encloses the internal components. It provides access for maintenance and adjustment of the valve.

Seals and gaskets

Various seals and gaskets are used to prevent fluid leaks between the different parts of the valve.

6 Precautions to Take When Using Pressure Relief Valve

01/

Before the pressure relief valve leaves the factory, its opening pressure should be adjusted one by one to the set value required by the user. If the user proposes the working pressure level of the spring, it should generally be adjusted according to the lower limit of the pressure level.

02/

Before installing the pressure relief valve on the protected equipment or before installation, the user must re-adjust at the installation site to ensure that the set pressure value of the pressure relief valve meets the requirements.

03/

You can adjust the opening pressure by changing the spring’s compression level. Simply rotate the adjusting screw within the spring’s working pressure level range, usually indicated on the nameplate.

04/

Before rotating the adjustment screw, the valve inlet pressure should be reduced to below 90% of the opening pressure. This prevents the valve disc from rotating when the adjustment screw is rotated, which may damage the sealing surface.

05/

In order to ensure the accuracy of the opening pressure value, the media conditions during adjustment, such as the type of media and temperature, should be as close as possible to the actual operating conditions.

06/

The conventional pressure relief valve is used to mitigate excess back pressure. When the opening pressure is adjusted after inspection (the back pressure is atmospheric pressure at this time), its setting value should be the required opening pressure minus the additional back pressure.

How to Maintain Pressure Relief Valve

Periodic inspections: Begin by visually inspecting the pressure relief valve and the area around it. Check for signs of corrosion, leaks, or damage. Make sure the pressure relief valve is properly installed and that there are no obstructions that could prevent it from operating.

Frequency of testing: The pressure relief valve should be tested periodically. The frequency of testing depends on factors such as the type of service, environmental conditions, and regulatory requirements. Typically, testing is performed annually or every few years.

Seal inspection: Check seals and gaskets for signs of wear or damage. Replace them if necessary to maintain a proper seal.

Cleaning: Clean the pressure relief valve and its components to remove any debris, dirt, or contaminants that could affect its operation.

Spring inspection: If the pressure relief valve uses a spring-loaded mechanism, inspect the spring for signs of corrosion, fatigue, or damage. Replace the spring if necessary.

FAQ

Q: What does a pressure relief valve do?

A: Pressure release valves are designed to open and discharge excessive pressure above the valve set point, either to atmosphere the pressure or pipe it away to a different location. Pressure relief valves are also commonly called circulating relief valves or pressure sustaining relief valves.

Q: What is the 3 rule for Pressure Relief Valves?

A: “When a pressure-relief vaIve is installed on a line directly connected to a vessel, the total non-recoverable pressure loss between the protected equipment and the pressure-relief valve should not exceed 3 percent of the set pressure of the valve.”

Q: What happens when a pressure relief valve goes bad?

A: Failure causes the valve to release pressure before the system reaches the maximum pressure or causes leakage and chattering. Troubleshooting the valve and the system for what's causing the issues is a safe practice.

Q: What is the difference between a pressure relief valve and a PSV?

A: PRV: PRVs open in a controlled manner to regulate pressure, allowing for gradual pressure reduction to maintain system stability. PSV: PSVs open swiftly and completely when the predetermined set pressure is surpassed, offering rapid depressurization to prevent catastrophic failures.

Q: Do you really need a pressure relief valve?

A: A pressure relief valve can protect your pump and internal plumbing from extreme water hammer. If there is a sudden surge of pressure, your relief valve will do its job and keep that excess pressure from moving to your truck's internal plumbing.

Q: What is the primary purpose of a pressure relief valve?

A: The primary purpose of a pressure Relief Valve is protection of life and property by venting fluid from an overpressurized vessel. Many electronic, pneumatic and hydraulic systems exist today to control fluid system variables, such as pressure, temperature and flow.

Q: Should pressure relief valve be open or closed?

A: In operation, the pressure relief valve remains normally closed until pressures upstream reaches the desired set pressure. The valve will crack open when the set pressure is reached, and continue to open further, allowing more flow as over pressure increases.

Q: Why is water coming out of the pressure relief valve?

A: Your water heater's pressure relief valve can start leaking for one of two reasons: either the valve was triggered to open because of excessive temperature or pressure, or the valve itself is faulty.

Q: When should a pressure relief valve be replaced?

A: As a general rule of thumb, we'd say that pressure relief valves should be tested every 12 months and replacements should take place every 3 to 5 years.

Q: Should the pressure relief valve be up or down?

A: Mount pressure relief valve in a vertical position, which means upright and with the spindle vertical. A valve installed in any position other than vertical might not perform correctly. For flanged valves, be sure to draw the bolts down evenly.

Q: What is the difference between safety valve and pressure relief valve?

A: A safety valve is a pressure relief device used to prevent the over-pressurization of a system. On the other hand, a pressure relief valve is a device used to relieve pressure from a system that is already overpressurized. The function of a pressure relief valve is to protect a system or component from excess pressure.

Q: Where should a pressure relief valve be installed?

A: Installing them to the mains supply after the main shut off valve will accurately control the system pressure. PRVs will also control the flow rate of the water running through the system – this protects fittings and appliances from experiencing blowouts of water at a fast rate at any outlet.

Q: What materials are used in pressure relief valves?

A: Common pressure relief valve component materials include brass, plastic, and aluminum. Various grades of stainless steel (such as 303, 304, and 316) are available too. Springs used inside the relief valve are typically made of music wire (carbon steel) or stainless steel.

Q: What psi should a pressure relief valve be?

A: The pressure rating of the relief valve must be equal to or less than the MAWP of the vessel. Most water heaters have an MAWP of 150 psi; however, some are rated higher, typically 160 psi. Some storage vessels have a lower pressure rating; they are commonly rated 125 psi.

Q: What pressure should a relief valve be set at?

A: The relief valve setting(s) should be at least 10% or 15-psig, whichever is greater, above the maximum operating pressure. Where unstable process conditions exist, this differential should be at least 10% above the maximum operating pressure or 25-psig, whichever is greater.

Shandong Yikaide Hydraulic Co., Ltd. is one of the most professional double counterbalance valve manufacturers and suppliers in China, specialized in providing high quality products and service. We warmly welcome you to buy customized double counterbalance valve made in China here from our factory.

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