Westinghouse check valve replacement

[Dark Wolf]

Last year I picked up a small portable compressor. The line after the 4th stage was leaking a little, so I am replacing the line. There is a check valve in the line labelled as follows:

Westinghouse
Air Brake Co.
USA
Ser No. cant quite make out number

AP 2 Check Valve
Assembly No.
820743
Operating Press
3000 PSI

I have looked online, but cant find one that looks like mine. So, those of you who are much smarter than I am on these, what do you recommend?

Thank you in advance!!

DW

 

[tbone1004]

I use Swagelok check valves, but Parkers are more than fine. Can't see the fitting on the inlet side, but the outlet should be a standard 1/4" JIC fitting.
You may not be able to find them with the JIC fittings directly, so you may have to adapt from NPT provided you have clearance.
Also note that there are two pressures listed when looking at check valves, working pressure and cracking pressure.

This one for example has a 6000psi working pressure and a 1psi cracking pressure.
Stainless Steel Poppet 6000 psig (413 bar) Check Valve, 1/4 in. FNPT, 1 psig (0.07 bar) | Swagelok
This one is 6000/10psi
Stainless Steel Poppet 6000 psig (413 bar) Check Valve, 1/4 in. FNPT, 10 psig (0.69 bar) | Swagelok

You do not want the cracking pressure to be too high because it causes backpressure in the system, so even though the pump may be pushing 3000psi, if the check valve has say a 300psi cracking pressure, you may only see 2800psi on the other side of it depending on the specific valve. I put the 6000/10psi versions on my compressor.

 

[Dark Wolf]

Thank you a ton for the info! Both sides are 1/4" male, what I thought were NPT. I can find no info on cracking pressure, but the compressor will run up to about 3500, so am I wrong in suspecting that it has a lower cracking pressure like you mentioned?

From my reading, having the check valve after the condenser and filter is preferred? This valve was located just before the condenser, so perhaps I should plan on relocating?

I apologize in advance if these are ignorant questions. But I am, well...ignorant on these compressors. I am learning a great deal, though.

Thanks again!

DW

 

[tbone1004]

Thank you a ton for the info! Both sides are 1/4" male, what I thought were NPT. I can find no info on cracking pressure, but the compressor will run up to about 3500, so am I wrong in suspecting that it has a lower cracking pressure like you mentioned?

From my reading, having the check valve after the condenser and filter is preferred? This valve was located just before the condenser, so perhaps I should plan on relocating?

I apologize in advance if these are ignorant questions. But I am, well...ignorant on these compressors. I am learning a great deal, though.

Thanks again!

DW

the top doesn't look like NPT. It looks much more like a JIC flare fitting, where NPT is usually threaded all the way to the end and doesn't have a nipple.

You should have a pressure maintaining valve or PMV after the filter which also functions as a check valve, but has the much more important function of maintaining pressure inside of the filter. The check valve usually goes before the condensor and filter so they can maintain pressure when the pump depressurizes while it's not being used.

 

[Dark Wolf]

the top doesn't look like NPT. It looks much more like a JIC flare fitting, where NPT is usually threaded all the way to the end and doesn't have a nipple.

You should have a pressure maintaining valve or PMV after the filter which also functions as a check valve, but has the much more important function of maintaining pressure inside of the filter. The check valve usually goes before the condensor and filter so they can maintain pressure when the pump depressurizes while it's not being used.

Understood!! Thank you so much!!

DW