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 .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.

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