Wafer Check Valve as a stop valve in process piping 1

[CW85]

Is a Wafer Check Valve, when subjected to reverse flow, a stop valve for the purpose of pipe design according to ASME Code 34.3? The main purpose of this question is to determine the boundry between system design pressures.

 

[samiam22]

I don't think it's wise to depend on a check valve as your only means of isolation. A manually operated valve should be included downstream of the check valve.

 

[CW85]

I agree that one should not rely on a check valve as a means of isolation, especially to work behind (say on a pump or control valve where you have a line break).

But with regard to defining the design temperature and pressure of a pipe system. That is the gist of the question.

Thanks for the comment.

 

[vpl]

Craig

You might want to post this in the ASME or valve forum. I work mostly with the nuclear codes and my quick gut answer would be "no."

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[saxon]

samiam, Never-Ever! depend on a check valve (I've never seen a check valve that doesn't allow some back bleed through even in ansi leakage class VI) to function as a block or stop valve. Unless of course you're willing to sacrfice some poor maintenance personnel along the way. Depending on service use single block, block with blind, double block and bleed, double block bleed and blind. Best yet, depressurize and drain the system.

Hope this helps.

saxon

 

[SooCS]

A check valve should not be used against pressure protection. But in defining spec break, it is acceptable to have a spec break at upstream of check valve, ie check valve has the same rating of the downstream piping and equipment. I am assuming the downstream equipment rating is higher than upstream equipment and you have other isolation valves at the inlet of the downstream equipment. However, you will require a PSV upstream of the check valves. In case the check valve leak. See API RP 14E or 14J.

 

[CW85]

SooCS, thanks for your input. It is the same conclusion that I have come to in reading various codes. I would further add that one should place a blocking valve (gate, plug or ball) directly against the check valve ALLOWING SUFFICIENT ROOM FOR CHECK VALVE FLAPPER MOVEMENT (either up or down stream; best downsteam) and have that block valve the same rating as the check valve (and downstream conditions).

Thanks for the code reference. CW85

 

[zdas04]

One trick I've been using the last few years is to put a block valve, then a short spool piece (with a thread-o-let and a blowdown valve), then the check. That way I can periodically (usually quarterly) shut the block valve and open the blowdown, if the short line section blows to zero, then the check is holding, if it doesn't blow down at all then the flapper is in the bottom of the pipe.

 

[CW85]

Zdas04. That is a good idea. It sounds similar to the tests done on double check valves.

 

[11echo]

CW85 ...You know you could use a STOP-CHECK valve. It acts both as a check vlv.(piston type) and a block vlv. Essentially all they are is a globe vlv. except the stem is not directly attached to the seat. Check it out ...my 2 cents. Mark

 

[tripper251]

I think you might consider A foot valve provided you have sufficent pressure.

 

[davefitz]

never rely on a check valve, since a workers's safety depends on positive shutoff eventually.

For a while , ASME I had required a "non-return" valve plus one stop valve to protect workers that might be inside a steam drum when a second boiler is in service. Problem was, they never defined a non -return valve and several boiler vendors supplied check valves instead of stop-check valves. Those units were not adequately protected , and the code was changed to require 2 stop valves with intermediate bleed.

In particular, if aunit operates continuously with the check valve either open or closed, corrosion deposits build up on the flapper axis/stem and the valve sticks in a certain position. And it is never leak tight.