Bellows Seal Gate or Globe
Bellows Seal Gate or Globe
(OP)
Hello 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
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





RE: Bellows Seal Gate or Globe
RE: Bellows Seal Gate or Globe
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
RE: Bellows Seal Gate or Globe
RE: Bellows Seal Gate or Globe
It 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.
RE: Bellows Seal Gate or Globe
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 1000 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 best
Conor
Bellows Manufacturing and Research, Inc.
https://bellowsmfg.com
RE: Bellows Seal Gate or Globe
Thanks for your reply. It gives me insight into design of bellows and different ways bellows can fail.