Bostich trim air cap 1512 over pressure and won't shut off

by John
(Charleston, SC)

Hi Bill,


I read your trouble shooting page and I'm not sure I follow or my compressor isn't following the exact symptoms...

The compressor builds pressure normally right up to 150psi which is where it's supposed to shut off. Instead, the pressure relief valve (unloader?) kicks open and spews air while the compressor keeps running. If I turn the compressor off and hold the valve shut with my hand, I can shoot a few nails but of course it runs out of pressure soon enough. That makes me think the relief valve is working properly but is it likely to be the check valve or the pressure switch? (I haven't figured out where the pressure switch is yet)

I took the end off of the check valve and the spring loaded seal looks ok to me...

Thanks,
John

Comments for Bostich trim air cap 1512 over pressure and won't shut off

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Jun 23, 2016
Thanks!
by: John

Thanks for the help! Great site!

Jun 23, 2016
PRV test
by: Bill

As you say, pull it out and push it in a few times.

As to the amount of air, I wouldn't worry about that unless you feel there is a blockage? Shouldn't be if you just cleaned it up.

The PRV is the second line of defense to preventing a compressor over pressure scenario. The first is the pressure switch that shuts the compressor off at the set point. If it fails, and the pressure grows, the PRV is set to release to drain pressure.

If you have doubts, replace the PRV.

Jun 23, 2016
PRV
by: John

That's a good thought Bill... Exactly how do I test it? I can pull it out and air leaks out... and I can push it back in and the leak stops, but it definitely seems different than how it used to work. What I remember from before is that the valve would release with a fairly loud burst of air and it would flow out in a big stream. I've tripped the prv while carrying it in the past. Now, it's not that easy to pull out and it's a smaller stream of air coming out of the valve. Is it supposed to react differently when it gets triggered by pressure vs when I manually pull it out?

Jun 23, 2016
Success!
by: Bill

Good stuff, John. Do please make sure that the PRV will operate. When you have a full tank, pull on the ring and then push it back in a few times, to make sure that it will actually let go if needed.

Jun 23, 2016
Success!
by: John

Thanks to both of you guys for responding! The prv was blowing out at around 155psi. Bill, I followed your suggestion and removed the prv, swished it around in some carb cleaner, rinsed it, dried it and now it seems to be working. Pressure just built up to 160psi and the pressure switch kicked in and shut the motor down.

I just need to reinstall both switch and valve with some thread compound of some kind. I notice the prv is leaking around the threads a bit.

Thanks again!


Jun 23, 2016
PRV or pressure switch
by: Bill

If the compressor nor cut out settings is 150 PSI, and the PRV is cracking open at 150 PSI, it's likely the PRV that is not working properly.

If the pressure switch cut setting is 150 PSI, and the tank pressure bypasses that and builds until the PRV lets go, then it is likely the pressure switch that has the issue.

Jun 23, 2016
PRV or P Switch
by: John

Doug,
You're right, my prv is marked as 160 psi. It's the original part as I'm the only owner and it's never been worked on.

Bill,
I *think* the prv was cutting out at 150 psi but I wasn't smart enough to watch that closely when it was malfunctioning. It might have been 160 psi. I guess I'll clean out the prv and put it back together and test it. If I understand correctly, if it goes past 150 psi without cutting off, it's a pressure switch problem but if the prv blows at 150 psi then it's a prv problem. Does that sound right?

Jun 22, 2016
PRV
by: Doug in s.d.ca

According to what I found, that should be rated at 160 PSI.

If yours is marked, pls confirm it's 160.

If it's marked less, it's the wrong part.

Jun 22, 2016
Bostich trim air cap 1512 over pressure
by: Bill

If the PRV is letting go at the same pressure as the cut out is supposed to occur, then you've got a failing PRV, John.

This model is oil free I believe. That being the case, it's not oil from the sump leaching into the air and fouling the PRV that's the issue, though it could still be something in the air flow that has "lubricated" the PRV internally, reducing the air pressure needed to crack it open.

The PRV should not let go at the normal compressor cut out pressure level, and often is set to crack 10-15 PSI higher than that normal cut out.

If you are not certain which compressor part is which, look at the pages about them on this site to better understand what each is and what each does.

With the tank empty and compressor unplugged, remove the PRV and rinse it in solvent. Pull and push on the PRV piston ring a few times then dunk it again.

After it dries, reinstall the PRV and power up the compressor. If the PRV lets go at the normal cut out pressure setting of the compressor again, it's time to get a new PRV, in my opinion.

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