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.
How Does a Pressure Relief Valve (PRV) Work?
A pressure relief valve opens to release fluid or gas when the pressure inside a vessel or system exceeds a predetermined level. The valve is typically spring-loaded and designed to remain closed under normal operating conditions.
When the pressure inside the vessel or system rises above the valve’s set point, it overcomes the force of the spring, and the valve begins to open. As the valve opens, fluid or gas is released from the system, and the pressure inside the vessel or system decreases. When the pressure drops below the valve’s set point, the spring force closes the valve.
The released fluid or gas is typically vented to a safe location, such as the atmosphere or a containment system. Once the air has been exhausted from the system and the pressure has fallen to its pre-set level, the pressure relief valve will close. The size of the valve determines the valve’s discharge capacity, the set pressure, and the characteristics of the fluid or gas being relieved.
How does a PRV control or limit pressure in a system?
A pressure relief valve (PRV) 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 PRV is a reactive device that responds to an overpressure 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.
PRVs 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.
Why Use a PRV?
The release of fluid or gas from the system through a pressure relief valve reduces the pressure to a safe level, thereby preventing potential damage or catastrophic failure of the equipment or system. PRVs help ensure the safety of personnel and the environment and minimize the risk of loss of production or property damage. Using pressure relief valves is critical to pressure system safety and can prevent costly and dangerous accidents.
Benefits of Using a Pressure Relief Valve (PRV)
- Safety – PRVs prevent overpressure situations that can lead to damage or catastrophic equipment or systems failure. The release of fluid or gas from the system through a PRV reduces the pressure to a safe level, ensuring the safety of personnel and the environment.
- Compliance – Many regulatory bodies require PRVs in specific applications to ensure safety regulations and standards compliance.
- Reliability – PRVs are designed and tested to provide reliable and consistent performance over various operating conditions.
- Cost-Effective – PRVs can prevent costly damage or downtime from overpressure situations, leading to cost savings and increased efficiency.
- Versatility – PRVs are available in a wide range of sizes, designs, and materials, making them suitable for use in a variety of applications and industries.
Overall, using PRVs is a critical component of pressure system safety and can provide numerous benefits in terms of safety, compliance, reliability, cost-effectiveness, and versatility.
Types of PRVs
Several types of pressure relief valves (PRVs) are available, each designed to meet specific application requirements. The most common types of PRVs are:
Spring-Loaded PRVs
These are the most common type of PRVs and are typically used in applications with relatively constant pressure. They operate by using a spring to maintain the valve in the closed position until the pressure in the system exceeds a set point, at which point the valve opens to release pressure.
Pilot-Operated PRVs
These valves use a pilot valve to control the opening and closing of the main valve. They are typically used in applications with fluctuating pressures, as the pilot valve can be adjusted to maintain a specific pressure range.
Balanced Bellows PRVs
These valves use balanced bellows to sense the pressure and control the opening and closing of the valve. They are typically used in applications where the process fluid is corrosive or tight shut-off and high accuracy is required.
Liquid Relief Valves
These valves are specifically designed for liquid applications and are typically used to prevent overpressure in pipelines or tanks. They allow a small amount of liquid to escape when the pressure exceeds a set point.
Safety Relief Valves
These are high-capacity PRVs typically used in applications where the potential for large-scale release of fluid or gas exists, such as in the oil and gas industry. They are designed to open quickly and thoroughly, allowing for the rapid release of pressure.
Pressure Relief Valves by Manufacturer
Bell & Gossett Pressure Relief Valves
Bell & Gossett pressure relief valves protect fired and unfired hot water vessels against hazardous operating pressures.
- Highest BTUH ratings available for valves in their class (790,000 to 5,999,000 BTUH)
- EPDM diaphragm operated (cast iron models) and diaphragm assisted (bronze models) have an effective area approximately five times greater than conventional “pop-type” relief valves to help overcome the effects of fouling
- Low differential between opening and closing pressures helps to prevent conditions under which system water might flash to steam and cause hammering
- Engineered in accordance with Section IV of the ASME boiler and pressure code for heating boilers with capacities certified by the National Board of Boiler and Pressure Vessel Inspectors
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McDonnell & Miller Pressure Relief Valves
McDonnell & Miller diaphragm-operated cast iron and diaphragm-assist-operated bronze ASME Safety Relief Valves are designed to protect fired and unfired hot water pressure vessels against over-pressure conditions. The diaphragm's "oversized" effective area generates a greater operating force which helps to overcome the effects of fouling. In addition, these valves feature a unique fail-safe disc with sufficient area to permit them to maintain their safety relief function in the event of a diaphragm rupture. These valves are designed, manufactured, tested, and labeled in accordance with the requirements of Section IV of the ASME Boiler and Pressure Vessel Code. They are offered in various capacities to permit a close match with the boiler output rating.
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Webstone Pressure Relief Valves
Webstone PRVs are designed for use with water, oil, glycol mix in residential or commercial residential plumbing, commercial plumbing, heating systems.
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Armstrong Pressure Relief Valves
Armstrong PRVs are built to high standards and offer many outstanding superiorities. Their extra large diaphragm assures positive action.
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How to Select a Pressure Relief Valve (PRV)
Selecting a PRV depends on the specific application requirements, including the type of fluid or gas, pressure range, flow rate, and operating conditions. Various pressure relief valves are available, including spring-loaded, pilot-operated, and bellows-type valves. Each type has its advantages and disadvantages.
To select the best fit for your application, determine the maximum flow rate the pressure relief valve needs to handle. This will depend on the size of the system and the amount of pressure that needs to be relieved. Maximum flow can be calculated using the system's maximum operating pressure and flow rate. Then determine the set pressure at which the pressure relief valve needs to open to relieve pressure; it should be set at a pressure lower than the system's maximum operating pressure to ensure safe operation.
The valve body and trim material should be compatible with the fluid or gas in the system to prevent corrosion or contamination. Your application will decide the valve's size, end connections, and other features. Consider the system's temperature, pressure, flow rate, and other parameters to ensure the valve can handle the conditions.
The valve you select must also comply with relevant standards, such as ASME Boiler and Pressure Vessel Code, API, or ISO. If you need clarification on any aspect of the selection process, consult with experts or manufacturers for advice and recommendations. They can help you select the best valve for your application.
It is essential to ensure that pressure relief valves are correctly installed, maintained, and tested to ensure their reliability and effectiveness in preventing overpressure situations.