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Crosby pressure relief valves have maintained leadership in overpressure protection for over 140 years. The direct spring-operated safety and pressure relief valves are among the world’s most widely used for oil and gas production and refining, petrochemical and chemical processing, and conventional and nuclear power. Crosby pressure relief valves maintain the industry’s most extensive and capable flow facilities for testing in air, steam, and water.

Crosby pressure relief valves have been on the forefront of overpressure protection for more than 140 years. The direct spring-operated safety and pressure relief valves are among the world’s most widely used in oil and gas production and refining, petrochemical and chemical processing, and conventional and nuclear power industries. Crosby pressure relief valves uphold the industry’s most extensive and capable flow facilities for testing gas, liquid, steam and multi-phase applications.

Crosby is part of Emerson’s pressure relief portfolio, a complete range of standard and customized solutions, whatever need you have for overpressure protection.

Emerson is an industry leader in pressure relief valve technology. A single point provider, they offer an extensive product range for reliable performance with lower valve life-cycle costs and unique solutions. Their unrivaled engineering and technical expertise results in pressure management products, application solutions and services that can positively affect your business, safety, operations and the bottom line. Their engineering teams have designed testing equipment and procedures that assure optimum valve performances under all service conditions.

Facilities have cryogenic flow testing capabilities down to -320°F / -196°C, and flow steam testing, making them amongst the largest in the world that are used for research, experimentation and control of emissions on relief valves, like Crosby’s.

Crosby’s H-Series direct spring-operated safety valves are the trusted and proven solution to thorough overpressure protection for steam safety applications such as economizers, steam drums, superheaters, reheaters and more.

Crosby’s J-Series valves provide high quality and dependable overpressure protection for air, gas, steam, vapor, liquid and two-phase applications in one simple design.

Crosby leads the way in pressure relief valve technology. Explore high quality and dependable overpressure protection and phase applications in their catalog of relief valves.

The 2700 Series pressure relief valve, also known as an expansion relief valve, features a superior design that handles air, steam, vapor, and liquid services. In addition, the fixed blowdown design simplifies testing and repair, and the maximum interchangeability of parts allows for easy maintenance.

Expansion relief valves, also referred to as PRV’s, pressure relief valves, or safety valves, are designed to protect system tanks from overpressure, therefore a vital component. Overpressure can be caused by several things, including failure of an expansion vessel or a pressure-reducing valve.

Carrying on pressure tests on systems consists of adjusting the valve set pressure, performing a seat l,eakage test and a backpressure test. The set pressure test is always performed first.

Expansion relief valves are used in a range of industry demanding applications where pressure levels are critical for operation. Applications and industries include:

Air pressure relief valves, also known as PRVs or safety release valves, are installed to prevent pressure buildup. The valve opens slowly to release pressure when the level becomes too high.

If the pressure within an air compressor system gets too high, one of the components inside could explode. Essentially, pressure relief valves are designed to prevent uncontrolled depressurization events from occurring, protecting surrounding nearby equipment and employees during overpressure events.

Test the secondary pressure zone of all valves exceeding 1" inlet size with air or other suitable gas at a pressure of at least 30 psi. Use a suitable leak detection solution to verify tightness of all gasket joints and vent/drain plugs.

Expansion relief valves are often known as pressure relief valves and for a good reason. They come with a preset pressure built into their design to ensure once the valve recognizes the pressure limit, it opens to release the pressure-flow (fluid of compressed air) safely.

It’s advisable to permanently mount pressure relief valves in a vertical position so the spindle sits correctly and can operate effectively. Overtightening the valve can cause damage to the inlet and cause leakage too. For the inlet piping, keep it short and direct, it should have a shorter diameter than the valve, and it should always be far away from turbulence or vibration in the operating system.

A pressure relief valve can encounter overpressure or failure for many reasons, but the most common reasons are typically blocked discharge in the system, contaminants like dirt, rust, or sludge, or even valve misalignment can cause the pressure relief valve to fail. Maintenance and proper inspection periodically can help eliminate leakages, allowing a safe environment for operation and the operators.

J series valves have a simple design that provides high quality and reliable overpressure protection for air, gas, water vapor, steam, fluid and two-phase applications

If the determined valve type and model are provided by the customer, the customer should correctly explain the meaning and requirements of its model, and sign the contract under the conditions that the supply and demand sides understand and agree.

Pressure relief valves (PRVs) are a critical line of defense for pressure vessel protection in the power industry. Generating facilities worldwide depend upon these devices to sense and quickly relieve overpressure conditions to avoid catastrophic damage during process upsets. To ensure these valves will perform as expected, mechanical engineering regulatory bodies mandate the valves be tested on a routine basis.

Some installations make the option of pulling the valve for servicing and testing very difficult. This is particularly true for large size valves, and in the nuclear power industry where valves may be located inside containment areas, making valve access particularly problematic. Fortunately, there is another approved method of testing relief valves for this situation, and this alternative solution is the subject of this article.

PRVs are relatively, but deceptively, simple devices. They consist of an inlet nozzle attached to the process, which is blocked by a disc held tightly on the nozzle seat (Figure 1). The disc is kept closed by a spring, with adjustments carefully made to dial in the setpoint of the valve.

1. A pressure relief valve (PRV) protects equipment by automatically opening to vent process media when the pressure in the inlet nozzle overcomes the downward force of the spring. Courtesy: Emerson

When the process reaches set pressure, the upward force of the process media offsets the downward force of the spring and the disc lifts off the seat. The process media is relieved through the valve outlet until pressure falls below the setpoint. At this point, the downward force of the spring overcomes the upward force of the process media, and the valve closes.

To ensure the PRV will function when called into action, the American Society of Mechanical Engineers (ASME) mandates relief valves be functionally checked on a routine basis. Typically, a plant will pull smaller valves from their installed position during process outages, and then inspect and test them in a shop environment to confirm they will function as desired and open at the proper pressure setpoint. However, this method of testing is not so easily achieved in certain cases.

Some relief valves are very large and/or located in difficult to reach areas. Others are welded into place and not easily removed from the process. Valves inside nuclear containment areas are particularly troublesome since access to these areas is usually restricted, with strict adherence to extensive protocols required for entry.

To handle these challenging situations, ASME provides alternate means of testing relief valves, as documented in ASME Performance Test Code (PTC) 25 Pressure Relief Devices. These test methods include in-service testing, which allows the plant to functionally test the relief valve without removing it from the process. This in-situ test method can be quite accurate and effective, but only if it is performed correctly with the right equipment.

ASME-approved, in-service testing allows the use of lift assist devices attached to the spindle of the valve with adapters, along with other test apparatus to perform set pressure verification testing. The equipment shown in Figure 2 allows a carefully monitored lift force to be applied to the spindle of a PRV until the disc lifts off the seat. The process pressure and the lift force are known, enabling this type of a computer-driven system to determine the setpoint of the PRV, and confirm that it falls within tolerance. This specific type of lift assist equipment is known as a set pressure verification device (SPVD).

2. A portable lift assist, or auxiliary lift device, allows a PRV to be functionally tested without removing the valve from the process. Courtesy: Emerson

A linear variable differential transformer (LVDT) is used to detect the earliest sign of valve stem movement, in the range of 0.020 inch, well below the point where the valve will go into full lift. At this time, force and pressure values are obtained, and the test is concluded to avoid wasteful discharge of the process media and minimize seat damage.

Perhaps the most important feature of an SPVD is a fully automated test execution system (Figure 3). This system incorporates an industrially hardened portable laptop computer running automated test protocols, including calibration and diagnostics. The computer can print out certified test results and be connected to up to five relief valves, simplifying and speeding test execution.

Some other types of lift devices are more manual and can only be operated by trained personnel, typically provided by the lift device vendor at considerable expense. However, a fully automated SPVD allows most plant technicians to perform PRV set pressure verification tests as needed. The most useful lift assist devices can be installed on a wide variety of PRVs, rather than just on those from specific manufacturers. Ideally, the lift device should be lightweight and easily adaptable to fit a wide range of relief valves.

SPVD is often the preferred choice to address a number of challenging PRV test issues. Some valves are very large or not easily removed, so an in-service test is clearly the least costly option (Figure 4). This can especially be true for large relief valves that are welded into the process piping.

4. Emerson’s Crosby SPVD is being used to perform an in-service test on this American Society of Mechanical Engineers (ASME) Section III Class 2 safety valve. Installation and testing of the SPVD does not restrict the PRV from operating should process conditions require the valve to open in service. Courtesy: Emerson

Inside nuclear power plants, many large PRVs are located within containment buildings, where access is extremely limited. For critical PRVs in these areas, SPVD lift assist heads and adapters can be permanently installed on the valves, with test cables routed outside the restricted zone and connected to a computer controller.

Since this type of lift device does not impact valve performance during normal operation or overpressure conditions, the PRV can still operate as necessary. Tests can be remotely performed from outside the containment building by simply plugging the cables into a test system and executing the test. Such an installation allows a plant to safely operate under normal conditions and test their critical PRVs on an as-needed basis, while avoiding any potential radiation exposure.

A well-designed lift assist device is a valuable addition to a plant’s PRV maintenance toolset. Every PRV is required to undergo regular in-service testing requirements as defined by the ASME Operation and Maintenance of Nuclear Power Plants code. The code permits use of lift assist devices to perform set pressure verification testing, which is particularly useful in situations where removing the valve from its installed position is not practical. The right lift assist device allows plant personnel to safely execute scheduled maintenance during outage events, or during operation in other cases, ensuring that critical PRVs are functioning per design with correctly adjusted setpoints.

A fully automated SPVD allows plant personnel to perform these tests consistently and accurately, freeing users to schedule and execute PRV tests, without the need for outside vendor involvement. This saves time and cost, and it removes dependence on a single vendor as a service provider. SPVD also provides a means for nuclear power plants to remotely test their critical relief valves, while avoiding exposure in containment areas.

—June DelGrossois the sales director for North America Nuclear and Navy at Emerson for its flow control products. She has worked for a variety of companies, filling roles such as Valve and Instrument Design Engineer, Product Engineering Manager, and Global Product Technical Leader.

Spring standardization. Standard Series 800 and Series 900 OMNI-TRIM® pressure relief valves are suitable for inlet temperatures to 750°F [399°C], using a 17-7PH stainless steel spring.

Series 800 pressure relief valves have an external blowdown adjustment allowing for short blowdown, smaller differential between operating and set pressures, and reduced product loss.