Confusion of pressure test statement in BS 1868 for Check Valves 2

[LJthien]

I am looking to your kind consultation of pressure test requirements which are written in BS 1868 (Chapter-36 Production pressure testing) as quoted below:
Quote:
All valves shall be pressure tested by the manufacturer before despatch in accordance with BS 6755-1, as below:
a) hydrostatic shell test;
b) hydrostatic seat test;
c) hydrostatic seat test at 25 % of the seat test pressure required for test b).
Unquote:
As I am not experienced in testing of valves, could you kindly advise if c) above requires a pressure test at 25% of pressure level of item b) above and why item c) is required whereas it could be covered by item b), in term of test pressure level?
Thanks a lot.

 

[mk3223]

By comparing to API codes of the valve design and testing, I would say that the BS testing requirements b) and c) as listed are be selected as an either-or option per conditions on the other section in the BS Code.

 

[bcd]

Item c) is a low pressure closure test. It is important to understand the pressure tests are a quality check, not a design validation test.

Sometimes, depending upon the seal type, it is more difficult for the valve to pass a low-pressure closure test. For example, if the seal is more compressed at higher pressure, then the valve is more likely to pass at higher pressure. In such cases, the low-pressure test is more discerning check of valve build quality. This is why low-pressure closure tests are done.

 

[LJthien]

@ mk3223
Thank you for your explanation.

 

[LJthien]

@ bcd
Thank you for your explanation.

 

[LJthien]

Dear brothers,

Thank you for your help.
Going further to check out the pressure test from API 598 I would like to ask your kind explanation if Backseat test and Closure test (Low-pressure or High-pressure closure test) can be done in 1 pressure test or itself are only 1 pressure test for valves that have the backseat feature?

The reason for my inquiry is the statement from API 598 Para. 5.3.2 as below:
"At the manufacturer’s option, the backseat test for valves that have the backseat feature may be either a high-pressure or a low-pressure test unless stated otherwise in the purchase order".

Warmest regards.

 

[bcd]

The backseat test is not applicable to check valves. Refer to Table 1 in API 598.

Examples of valves with backseats are gate and globe where the stem can be raised until a shoulder on the stem contact the body, blocking pressure from reaching the stem packing. By blocking pressure to the packing when fully open, risk of packing leak is decreased. Also, allows for the packing to be replaced while the valve is in line.

Per Table 1 of 598, required tests for Check valves are shell and high pressure closure. Low pressure closure is optional and is done when requested by the purchaser.

 

[LJthien]

@ bcd.

I got your point clearly for check valves.
Just taking this opportunity I would like to learn more about gate valves as well, the valve have the backseat feature like what you emphasized. So could you advise me if "Backseat test and Closure test (Low-pressure or High-pressure closure test) can be done in 1 pressure test or itself are only 1 pressure test for gate valves"?

Thank you very much for helping me here.

 

[bcd]

I do not understand your question. Per API 598, the backseat test may be combined with the shell test for valves DN 100 (NPS 4) and smaller. API 598 does not specify the test order sequence. Tests can be combined as explained for the backseat and shell test. I do not what you mean when asking if low pressure and high pressure closure tests can be done in one pressure test. I would say "no" because the test pressures are different. But, if you are asking if it is possible to do both high and low pressure tests in the same test rig/fixture/set-up, yes, this is possible.

The scope of this thread is changing with your last question so best to start a new thread under a new topic heading for everyone's future benefit.

 

[LJthien]

@ bcd
I'm really sorry for confusing you.
I get to know about check valves already, thanks to your explanation.
It was my additional query about gate valves, my concern exactly is the statement in API 598 Para. 5.3.2. I would like to consult you if "the backseat test may be either a high-pressure or a low-pressure test" for gate valves.

Once again, thanks a lot for your help.