Water Service Valve Used in an Air application

[tlona]

The contractor has installed a water service butterfly valve in a compressed air system application. The valve is in a bypass line around an air filter bank and will be normally closed during operation to force the air through the filters. Can I use this valve even though it is not rated for air service? What is the real issue? During operation the pressure drop will be inches around the valve and it is rated for 200psig. The vendor had no real answer other than it is not rated for air. Problem is we do not have the time to replace the valve. Thank-you

 

[Cockroach]

It should be okay, noting the low pressure rating, ANSI Class 150, and the valve geometry, a butterfly. In general the seat configuration for a compressible flow application is slightly different than incompressible medium, and the material selection for the elastomers is different.

You could get away with this on ball valves as equally as a butterfly, but not a gate or globe type arrangement. My only worry is the seat arrangement when the valve is cracked, you may blow out the element due to the migration go gas behind the rubber and into the interstitial voids of the gland. Hence the different seat geometry for gas verses liquid applications.

Hope this helps. Good luck with it.

Regards,
Cockroach

 

[tlona]

Good explanation. Thank you.

 

[MiketheEngineer]

I am sure the above gentlemen are correct - this is not my area of expertise - BUT what if something goes wrong.

Who gets hung out to dry - YOU DO!!..

Just keep that in mind...

 

[zdas04]

Mostly when I see valves or fittings not rated for gas service I look to the metallurgy instead of the elastomers. We had some "pot metal" (that term does not have a specific meaning, just cheep, quick cast stuff) valves in the 80's that would come apart with shrapnel if you increased the pressure when they were cold. The "with shrapnel" part was the reason that they were banned in our field. At summer temperatures they seemed to hold pressure just fine, but pressure transients when they were cold were not much fun.

The ones that failed in liquid service mostly "just" made a mess on the ground. The ones that failed in gas service were pretty scary and quite dangerous.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[tlona]

Thank-you all for the feed back. I also learned the EPDM seat drys out and cracks when used in a compressed air application. Thank-you all for your feedback. This valve is REJECTED!!!!

 

[btrueblood]

"the EPDM seat drys out and cracks when used in a compressed air application"

It shouldn't, else it's not really EPDM. EPDM is listed as an elastomer of choice in the Parker O-ring handbook for air at 200F and below.

 

[moltenmetal]

EPDM is fine with air and water. It's not much good with oil, though. Nitrile (buna) would be preferable in a compressed air application if there was any comrpessor oil around.

 

[btrueblood]

Agree, molten. But with oil exposure, the epdm would still not dry out, just get really gooey.

 

[rconner]

While not saying it is the case in this application, one must be aware as well that in some air/gas applications temperature can be more extreme (e.g. with compression near blowers etc.) than it is in normal water services.