Bubble tight test 3

Gentlemen:

Could some one explain what is meant by a bubble tight valve? How is the test done for bubble tightness?

many thanks

bob

 

[TD2K]

We used to test critical valves used for equipment isolation by putting pressure on the upstream side (normal operating pressure) and checking for leakage through the valve.

We'd essentially do a hydrotest on the upstream valve and check for leakage past the seat.

If you want to use compressed gas, you can put a flange with a connection going into a water filled tube so you can check for bubbles showing leakage is occuring (I'm not crazy about using compressed gas for high pressures).

 

[joeswoes]

I am not familiar with a test procedure or standard which defines "bubble-tight". ANSI/FCI 70.2 provides testing and leakage rates for control valves, but the tightest valve, Class VI has an allowable leakage rate. It must be a mutually defined and accepted criteria between vendor and customer. If anyone knows otherwise, I'd also be interested.

 

[cranekiran]

Bubble tightness is a wide terminology which simply means zero leakage when the valve is in close position.Now if the medium is water then the valve should have zero leakage at twice the rated pressure if the testing is based on AWWA Standard.i.e If the line pressure is 10 bars then the valve should be bubble tight at 20 bars at closed position for 10 minutes,This test is also known as seat test in the case of Rubber seated butterfly valves.The method is :-

The Butterfly valve is mounted on a test flange or spool piece where the hydrostatic pressure is built up to the test pressure at closed position.The other end of the valve is thoroughly cleaned with compressed air so that the disc and the seal is free from dust and watery compounds;This is done because you have to visually see the contact area properly.Now,The contact area of the disc and seal should not have any leakage or drop in pressure which can be verified by a pressure gauge(Even a delayed sweating is not permitted).This test is done for the time based on the standard you apply for the test procedure.

I would be glad to know from the members the procedure applied if the media is other than water and for valves other than Butterfly valves.

 

[Hush]

For API 6A valves I've only seen the term applied to gas testing. Following hydrotest the valve is submerged in water tank and tested with nitrogen to working pressure, both shell and seat(s). If you see a bubble the valve fails. Hence bubble tight.

 

[kstaylor]

Check API-598 for the allowable leakage rates in either bubbles per minute or drops per minute for testing with gas (i.e. air or nitrogen) or water respectively.

 

[hammerr]

I agree with cranekiran. The term bubble tight by itself doesn't mean much more than a gas leak test. Normally there is a following description like: seat leakage is bubble tight against 60psig Helium, or for the case of B16.34 type valves air/Nitrogen media is often assumed. If there is no qualifying description other than "bubble tight", I assume FCI 70-2 class 6 type leak test procedure (50psig air with tube under water) and bubble tight as one rating step tighter than the class 6 rating.

 

[Hush]

bob98,

What application is your valve? It seems bubble tight has different meanings depending on the industry your in.

 

[mehrishi]

I think bubble tight shut off is basically for soft seated valve where leakage is 0.It can be checked by low pressure test by air (pneumatic seat test at 6 Kg/Cm2)

 

[valvetech]

Ansi Class VI standard is 0.15 ml/min (1 bubble per min)is considered bubble tight. the test is 50 psi air or nitrogen through the valve and the valve does not pass more than one bubble per minute.
But in the field even though the valve passed the test, it may pass more than one bubble per minute, since the actual operating conditions may be different than the test conditions.

 

[kevinf]

A bubble-tight valve is one which has a soft seat (EPDM, teflon, etc.) and provides zero leakage shutoff. Standard "rubber" seated butterfly valves are considered bubble-tight.
A bubble-tight valve is tested by putting the valve in the closed position and applying the rated differential pressure, using water typically.

 

[hammerr]

Bubble tight means no bubbles for the duration of the test. Not the same as class VI which allows x number of bubbles per minute depending on the size of the valve. Water media doesn't count as a bubble test. Water infers a liquid which makes drops. Not bubbles.