Check Valve : API 6D vs API 598

[h9.hanin]

Dear expert,

Is anybody have experience with check valve API 6D?
Based on API 6d, leakage rate shall refers to ISO 5208 (1993) rate D (metal seat dual plate check Valve).
But, the vendor states that this rate is very low.
They propose us to use API 598 as acceptance for leakage.
My question is :
Is it still possible to apply rate D ISO 5208 as acceptance criteria for leakage rate on Metal seat Dual plate CKV?

Thank's
~h9~

[Pedro_Suarez]

Rate D is very low. If I were you I would demand rate A, but it is up to you. You have to take into account the responsability of the service and health and safety at work.
If it is neccesary, change the kind of valve (seat).
You can download ISO 5208 and EN 12266-1 here:

[link Point to another website Only the registered members can access]

[h9.hanin]

Thank you for your response Pedro,

Actually, we can easily achieve Rate A (no leakage at all) if we change the metal seat to soft seat (elastomer). But then, as per approved spec, we shall provide dual plate check valve with metal seats.
Several vendors can not fulfill the leakage rate as per API 6D (refers to Rate D ISO 5208). The vendor that has "the best leakage rate" can only propose Rate F as per ISO 5208 (similar with API 598).
Do you have any comments?

Thank you
~h9~

[h9.hanin]

Thank you for your response Pedro,

Actually, we can easily achieve Rate A (no leakage at all) if we change the metal seat to soft seat (elastomer). But then, as per approved spec, we shall provide dual plate check valve with metal seats.
Several vendors can not fulfill the leakage rate as per API 6D (refers to Rate D ISO 5208). The vendor that has "the best leakage rate" can only propose Rate F as per ISO 5208 (similar with API 598).
Do you have any comments?

Thank you
~h9~

[Pedro_Suarez]

I know that it is very difficult or almost impossible to achieve high rates in this case. For better understanding you only have to think about the use of a gasket in flange connections. I would explain the problem to the client (or the user) and I would wait until the client makes a decision. The client should know better than us the service conditions and the reason of his technical specification, it maybe possible that he can suggest you other manufacturers and models.