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Bellows Seal Gate or Globe
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(Mechanical)
(OP)
12 May 15 16:13Hello Everyone,
I am new to the Valve industry and learning different designs and standards. Just came across Bellows Seal Gate and Globe. I read SP-117 and a few drawings and see that Bellows undergo Compression and Extension cycle under pressure. Recently, I observed leakage through Bellows Seal with fluid leaking through the bushing. Can someone explain more on Bellows seal from its Design point of view and how they handle fluid pressure?
Thank you
Replies continue below
(Mechanical)
18 May 15 19:34What kind of fluid are you dealing with and at what temperature? Mechanical seals such as these are rated for pressure based on a specific gravity and temperature of the fluid. The lower the SG or the higher the temperature, the lower the pressure rating will be.
(Mechanical)
Contact us to discuss your requirements of angle bellows globe valve. Our experienced sales team can help you identify the options that best suit your needs.
18 May 15 21:18"I observed leakage through Bellows Seal with fluid leaking through the bushing."
This should not happen unless there is a rupture of the bellows.Look here: www.google.com/search?q=bellows+seal+gate+valve&am... =_
Sometimes its possible to do all the right things and still get bad results
(Mechanical)
(OP)
19 May 15 13:38Apparently, the bushing came loose due to pressure. There was no fluid leakage through the bushing(it was wrong I said that in the first post). To me, it looks like the fluid load being applied to bellows transferred the load up until bushing making it loose. This was surprising since this being a Gate valve wherein the axial load is lesser(as compared to globe). That's why I'm trying to understand the way Bellows seal handle fluid pressure. There was no rupture of the Bellows here and this happened during the hydro test.
(Mechanical)
19 May 15 14:58It is still a bit unclear how the different parts are located and being mecanically moved by spindle movement and fluid pressure relative to each other.If the bellows are non-leaking apart form inlet and outlet openings for spindle and bushings, there could possibly be an operation - caused 'wrong' movement of the spindle.The spindle could be forcing the bellows to stretch or compress (or skew) more than allowed for by the construction. An unprecise operation or forced operation against poorly machined or placed/dimensioned end-stops, sealings or bushings could give the result you are describing.
(Aerospace)
9 Jun 15 17:47There could be several issues here so I'll hit on a few and you can look further into it.A. Pressure Trust - When a bellow is put under pressure it produces a pressure thrust (P x Ae), where P is the Pressure and Ae is the Effective Area of the bellows. If the connecting ends are not property designed to deal with this, issues will arise.B. Displacement - The bellow is designed to displace, ensure the displacements have been calculated correctly and compare to the design displacements of the bellows.C. Cycles - Bellows are designed for a certain number of cycles. For your industry it is usual to try and design for 100k cycles. Other industries go a low as cycles. Determine how long it takes for your valve to reach 100k cycles (or your design number of cycles) so you know how frequently the bellow needs to be changed out. Understand each induced stress in a bellow is considered a cycle (be it pressure, thermal or displacement).D. Vibration - Observed if there is vibration in the system. The natural frequencies of a bellow can be calculated or provided by the manufacturer. Compare these to frequencies produced in the system to ensure you do not have resonance.That will keep you moving in the right direction for now.All my bestConor
Bellows Manufacturing and Research, Inc.
https://bellowsmfg.com
(Mechanical)
(OP)
11 Jun 15 17:59gerhardl and bellowsmfg,
Thanks for your reply. It gives me insight into design of bellows and different ways bellows can fail.
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The bellows globe valve is also called the bellows seal globe valve. Through automatic roll welding, a metal barrier is formed between the flowing medium and the atmosphere to ensure zero leakage of the valve stem. Compared with the traditional globe valve, the bellows seal one has the following advantages:
1. The bellows globe valve has a long service life, low maintenance and low operating costs. Robust bellows seal design ensures zero leakage of the valve stem and provides free maintenance.
2. The opening and closing torque of valves is small, which reduces labor intensity and can drive any form of the actuator, convenient for remote control.
3. The appearance is beautiful, and the valve passageway has smooth streamline, which reduces the flow resistance coefficient of the valve. Hence, this valve is a high-quality and energy-saving product.
4. The outside sealing of the valve adopts the bellows seal, graphite gasket seal and stainless steel gasket seal, which is reliable and can be used for a long time without replacing the sealing packing. The leakage caused by the industrial globe valve not only pollutes the environment, but often causes heavy personal and property losses. The bellows seal one is much safer and more stable. And foreign advanced standards are strictly adopted in its design and manufacture.
The Application of Bellows Globe Valves
The bellows globe valve has no leakage, so it is safe to be used for the high-risk medium.
Bellows globe valves replace the packing seal with closed bellows which can be stretched and compressed, effectively preventing leakage caused by packing losses. Generally, these valves are used for the transmission of the medium with strong permeability. For instance, valves for hydrogen systems. As long as bellows are not damaged, the valve leakage generally not occur. However, the general globe valve is sealed with packing, easy to cause leakage.
For more information, please visit ANSI Bellows Seal Gate Valve.