Duo Check Valves. How Leak test it? 1

[Analista]

Good day.
We designing a bildge-ballast system for a ship River and selected valves duo check for suction lines (Low weigth). Crane Duo Check valves were select in ASTM A395 with metal seat and interior stainless steel .
They came to the worshop and the officers performed a "proof of tightness," water without pressure on the side of the springs and found that the fluid is not retained.
They are determined to return the valves to the supplier (Crane-WO supply), but I'm not sure that this is a good practice to test the tightness of the valve.
---
What is the problem?
We made a bad choice? this is not the correct way to test the valve? Should be tested with a minimum pressure? The material or the seal is not adequate?
(Design pressure is 6 BAR)

 

[gerhardl]

Any check-valve, both soft and metal seated, will require a certain amount of pressure to reach the factorys stated closure thightness. (This will for softsealed valves (non-metal closure) often be in the range of 2 meter water column. - I have not checked Crane metal seated, but cannot imagine this to be below 1,5m???)

The factory will be able to give you precise information on the important facts here:

a) Required pressure (water column) for thight closure
b) Rate, specification ond explanation on how thight and how to test and measure for max and min pressure.
c) Information on test procedure at factory and if every valve is tested or not-
d) Any generalcertification on the valve (Lloyds, Veritas etc.) approval, material and pressure test certification.

If theese points concur with the buyers inquiry, and no extra test is required or mentioned, the question is still if the test done at yard can be accepted by the supplier and factory.

If the test done is outside above parameters you can state this.

If the test validity is OK, the question is if the valve was completely undamaged, and no impurities present. For metal seated valves hairthick scratches and small impurities will easily give some leakage at low pressures.

To clarify in this case, ask first if the factory is willing to accept a new test and consquences if not approved.

Then ask for new test for a number of valves done under supervision of you or neutral third part, and under agreed technical conditions and actions afterwards according to technical results.

 

[BigInch]

Maybe you didn't pick the wrong valve, you are just requiring an impossible performance criteria for the valve you picked. If you want no leakage, don't use a check valve. If you need one-way flow and and no reverse flow or reverse leakage of any kind, back up the check valve with a positive shut-off block valve.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[gerhardl]

BigInch, I agree. I have seen several cases where 'impossible things' were required solved by check valves , especially on suction side of pumps, both for keeping drop-thigt and for delayed (not opening not before a relatively high opening pressure was reached).

As you suggest, such cases might be solved in a better way by including shut-off valves , different layout, or extra filling of suction lines from above before pumpstart.

 

[BigInch]

There's a lot of people out there that think check valves provide positive shutoff. They might, but they never should be counted on to do it when you need it.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JimCasey]

Good observation, BigInch.

People think nothing of putting a 48" cheater bar on a gate valve to get it to shut off tight, then they expect drop-tight closure from a check valve with a single hairpin spring. The check-valve is primarily designed to offer little resistance in the forward direction, and that means there is not a lot of seating load to give tight shutoff.

I like the duo-chek design. I got to know it when it was manufactured by TRW/Mission. It is important to note that the resilient seat is a option, not standard.

 

[Analista]

Thank you very much everybody.
Very good advice. decided to conduct some tests to pressure of work, putting them in a test bomb and the results were expected, there was no leakage.
Then the valve will be instaled.

 

[htownvalve]

I've sold Duo-Checks at my last job and know that these things just slow down flow. Never count on them for tight sealing. Saw many in the field that when they were removed from the line one or both of the plates were gone. Sometimes the center pin as well. There is a reason they are so cheap. Keep that in mind.