We’ve had a couple of recent posts about pressure relief valves (PSVs), including Improving Pressure Relief Valve Safety, Reliability and Performance, and Accurately Monitoring Pressure Relief Events. In them was some discussion about conventional PSVs and ones with bellows.
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I wanted to learn more, so I found this great explainer video on YouTube. The video, What’s the Difference Between a Conventional and Bellows PSV?, is by Matt Anderson, a Chemical Engineer with a major U.S. refining company.
He shares how a conventional PSV is affected by the backpressure of the header, into which it relieves pressure. This PSV opens based on the differential pressure between the protected vessel and the downstream backpressure in the relief header.
In a balanced bellows PSV, the metal bellows isolate the area above the disc from the superimposed backpressure. Matt references the Pressure Relief Valve Engineering Handbook that defines bellows as:
…a flexible component of a balanced direct spring valve used to prevent changes in set pressure when the valve is subjected to a superimposed back pressure, or to prevent corrosion between the disc holder and guide.
Emerson’s Marcelo Dultra shared with me that a challenge in the bellows’ design is that they can leak from wear and tear over time. The news, Emerson Reinvents Pressure Relief Valves to Improve Performance and Reduce Emissions, describes Bellows Leak Detection, which:
…addresses the problem of bellows failures, which are challenging to detect and often remain unnoticed for years until removal of the valve for periodic service. Leak detection and repair (LDAR) programs may include PRVs, but their target sources for leakage detection are flanges or valve seats, so bellows ruptures will generate fugitive emissions through the PRV bonnet vent that may not be in the LDAR scope. In addition, PRV installations are often difficult to access and in hazardous locations, making leak detection difficult.
The Bellows Leak Detection solution is a safer and more efficient method for detecting bellows failures and emissions. It consists of a backup piston and a Rosemount™ wireless or wired pressure transmitter. The backup piston can reduce emissions by over 90% in the event of a bellows rupture because it has a much smaller clearance than a standard bonnet vent, and it ensures balanced operation. The pressure transmitter provides instant timestamped notification of bellows failure and emissions volume data in real-time.
And better yet, the bellows can be eliminated.
The Crosby Balanced Diaphragm can replace bellows in PRV applications to address these [bellows failure rate between 2% to 6%] and other issues. Its innovative design extends the backpressure limits from 60% to 80% and increases the Kb backpressure correction factor by up to 15%, expanding the application range of spring-loaded PRVs. The Kb factor is used to size PRVs when they are installed in closed systems subject to backpressure. Extending the backpressure limit and increasing the Kb factor often permits the use of smaller valves. In addition, diaphragms are inherently more resilient than bellows for higher backpressures and rapid cycling applications.
Visit the Reinventing Pressure Relief Valves page to request more information and connect with Emerson experts to discuss your applications.
If you want to learn more, please visit our website Bellow Seal Valve.
What is a Bellows Sealed Shut-Off Valve?
The bellows-sealed shut-off valve is a highly specialized valve used to control flow rates in many industrial processing systems. It is suitable for various working condition pipelines in petroleum, chemical, pharmaceutical, fertilizer, electric power, and other industries to cut off or connect pipeline mediums.
The critical component of a bellows sealed sanitary shut-off valve—metal bellows—is welded at its lower end with the valve stem component and at the higher end with the connection plate, forming a metal barrier between the fluid medium and the atmosphere to ensure zero leakage of the valve stem. The valve flap and the sealing surface of the valve body undergo precision grinding and a 100% pressure test after assembly to achieve zero leakage. As an auxiliary sealing, the stuffing box remains on the bellows, increasing reliability and safety. The metal bellows of these high-pressure valves are multi-layered structures. Through hydraulic forming, these durable units can be guaranteed to perform at least ten thousand on/off full strokes at maximum pressure.
Six Advantages of Bellows Sealed Shut Off Valves
The bellows seal design eliminates the shortcomings of rapid aging and easy leakage of common valve stem packing seals. It improves energy efficiency, increases the safety of production equipment, reduces maintenance costs and frequency, and provides more outstanding cleanliness and safety, making these valves useful in many industrial working environments.
Sealed by the bellows and packing, if the bellows fail, the stem packing will remain intact and leak-free.
The robust structural integrity provides reliable sealing and excellent leakproof performance.
Leak-free performance results in no fluid loss, which reduces energy consumption, promotes environmental friendliness, and improves plant equipment safety for employees.
The sealing surface is coated with co-based cemented carbide for wear resistance, corrosion resistance, friction resistance, long service life, reduced maintenance time, and reduced operating costs.
The sturdy and durable bellows seal design ensures zero leakage of the valve stem and provides maintenance-free conditions.
The stop valve stem is quenched and tempered, and the surface is nitridated for superior anti-corrosion and anti-friction properties.
Conclusion — Sanitary Shutoff Valves
These sanitary shutoff valves are pneumatically or manually operated and offered in a wide variety of body configurations. When stopping or diverting flow in a processing system, this series single-seat valve line provides a flexible and reliable solution.
Adamant Valves is a trusted supplier of bellows sealed shutoff valves. We can provide a custom build, or you can choose from our existing inventory of body and disc materials such as AISI 304, AISI 316L, 304L, and 316 materials. Automated or manual operation valves are available according to your needs.
Thank you for reading our article. We hope it can help you better understand the advantages of bellows sealed shut-off valves. If you want to learn more about sanitary valves, we would like to advise you to visit Adamant Valves for more information.
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