Bellow Seal Valves Piston Valves Conventional Valves Primary stem seal Metallic Bellow Piston Ring Gland Packing Secondary stem seal Gland packing None None Stem Leakage Not Possible since Metallic Bellows are designed to last several thousands cycles Occurs as soon as the ring wear out. Very common. Due to friction between stem occurs within a few cycle no matter which make valve or quality of gland packing Packing Replacement Not applicable Rings need to be changed frequently Packing needs to be replaced very often Replacement Cost Not applicable Very High High Media Loss Zero Loss. As the isolation is by metallic bellows, leakage (in ppm) is not possible. Large in case of leaks Considerable amount through gland leakages. Normally large amount when leakage remains unattended. Equipment Downtime Nil Very High for replacing rings Very high for replacing gland packing Maintanance Cost often Nil High as rings need to be changed atleaset once in six months Very high, Gland packing needs to be replaced / repacked. The cost along with equipment down tme, man hours spent act is very high. Valve Life High-in years Low VeryLow - in -months. Due to leakage through gland, certain parts erode, making the valve irreparable after some months. Safety Can be used safely for almost any media Can be used for limited medi like steam, hot water Highly unsafe when the media is hazardous / poisonous Cost Comparatively higher initially but lowest total cost of ownership High compared to the benefits Initially low but very high after some years if cost pf packing, down time, man-hours spent, number of valves replaced act. are taken in to account.

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Bellows Seal Gate or Globe

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Bellows Seal Gate or Globe

Bellows Seal Gate or Globe

engineer

(Mechanical)

(OP)

12 May 15 16:13

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

Replies continue below

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RE: Bellows Seal Gate or Globe

venividivici

(Mechanical)

The company is the world’s best Forged Steel Bellow Seal Globe Valve supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

18 May 15 19:34

What 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.

RE: Bellows Seal Gate or Globe

pennpiper

(Mechanical)

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:

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

engineer

(Mechanical)

(OP)

19 May 15 13:38

Apparently, 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.

RE: Bellows Seal Gate or Globe

gerhardl

(Mechanical)

19 May 15 14:58
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.

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

bellowsmfg

(Aerospace)

9 Jun 15 17:47
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 best

Conor

There 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

RE: Bellows Seal Gate or Globe

engineer

(Mechanical)

(OP)

11 Jun 15 17:59

gerhardl and bellowsmfg,
Thanks for your reply. It gives me insight into design of bellows and different ways bellows can fail.

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