prv valve keeps popping open on a Central Pneumatic 2 h.p.

by Wayne
(Boise, Id.)

I have a Central Pneumatic 2 h.p. with 8 ga. tank. Every time I use it lately the prv valves pops open at around 50 or 60 p.s.i..


It has adequate oil (which brings another question to mind), It was low on oil the other day and all I had was some lawn mower oil so I put some of that in, was that okay to do?

Anyway I am unsure of why the p.r.v. valve comes open at only 50 p.s.i.? I replaced it with a new one, are there different sizes?

Lastly I should mention that it was still popping open before I added oil and put new valve on.

When should it pop open, at 125 p.s.i.? That's what the specs say on the side of the tank for maximum. What do I need to do to fix this without buying a new one?
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Wayne, many questions.

Regarding oil, see the pages about oil on this site. I doubt that lawnmower oil is suitable for your air compressor, unless it has exactly the same characteristics of compressor oil, which is what you should use.

As to the PRV, no, it should not open at 50 PSI. This would lead me to think that the PRV has gone bad... but, since you put a new one on already (it's the PRV cracking pressure that determines if it is the correct one for your compressor) and it is still popping open at 50 PSI, then unless the new one has a cracking pressure of 50 PSI, then it's likely not the PRV itself that is causing it to open.

You don't provide a model number, so I cannot guess at what might be causing this, not knowing how the compressor is configured.

Bill


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Apr 23, 2014
PRV (valve is redundant)
by: Doug in s.d.ca

Are you sure the tank pressure is only 50psi or so?

Sounds like you may be looking at regulated pressure...or the gauge is broken...

and the pressure switch is cutting off at much more than 125psi...

and blowing the PRV (this is why it's there, so the tank doesn't blow up if the compressor fails to stop).

Typically, PRVs you'd buy locally will be be about 140-150 psi, so if you replaced it, it's very likely something else is wrong.

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Central Pneumatic air compressor model 95386 possible capacitor issue?

by Shane
(Bowling Green KY)

Central Pneumatic air compressor 93586

Central Pneumatic air compressor 93586

I have a Central Pneumatic air compressor model 95386.

I got it used. It worked well for a few months. Then it started tripping the reset switch. I could reset it, it would run fine.

Then I started to notice the reset become more frequent and prior to it tripping I could see smoke coming from the capacitor.

It only has one capacitor.

I found a manual for it online and the specs showed the cap needed to be 250v 150 uf. I bought a new one and it does the same thing. I looked online and someone posted that some compressors have a centrifugal switch that cuts off the capacitor once the motor starts.

So I tested it by resetting it and once the motor was running full speed I pulled one lead from the cap. The pressure built up properly then shut off.

I reconnected the wire to the cap, pulled the safety valve to release some air. The compressor started back up to build pressure and I pulled the lead off the cap again and once again it built up to the proper pressure.

I did this sequence several times and worked fine every time.

I then pulled the motor (to the best of my ability) but could not find the centrifigal switch. Is it possible that something else is used to disconnect the cap instead of a centrifugal switch?

I also saw that there are run capacitors and starter capacitors. The one that I bought as a replacement is a Vanguard BC-145M-250.

Sorry this got so long but wanted to be as thorough as I could.
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I'll have to leave the issue of centrifugal switch to the compressor motor folks, Shane. I hope some will read this and comment for you.

One thing you don't comment on is how you are powering your air compressor?

Perhaps, as a comment here, you could tell us what the breaker amperage is for the circuit supplying the air compressor, how many other electrical devices are pulling power from the same circuit or if you are using an extension cord or power bar? All of these have an effect on the motor operation, including the capacitor.

Cheers,

Bill

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Apr 14, 2014
start cap
by: Doug in s.d.ca

You almost certainly have a bad switch, from your description.

I suggest you google "capacitor motor switch"

That should get you to a fairly comprehensive article by Fluke on troubleshooting them.

Good luck

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Adjusting pressure on model number 69434

I have a model number 69434 compressor and I need to know how to adjust the output pressure
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Friend, your question could apply to the pressure switch, which as you know after reading the page on pressure switches on this site, is the device that turns the compressor on when the tank pressure reaches the cut in pressure, and turns the compressor off when the tank pressure reaches cut out.

If you are trying to adjust these pressures, the how to is referred to on that page.

Or, are you trying to adjust the output pressure of the air in the air line to your air tool?

That information is covered in detail on the air regulator page on this site, too.

Have a read of both, and if you still have a question, add it as a comment here.

Cheers,

Bill

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central pneumatic 67847 wont run more than 2 seconds

by ashley
(texas)

Central Pneumatic compressor 67847

Central Pneumatic compressor 67847

I have a central pneumatic 67847 air compressor and it trips every two sec. Would the wrong oil make that happen i think we put motor oil in it
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Motor oil is definitely not for compressors, as it has detergents and other additives that are evidently not good for compressors.

Having said that, you do want to drain the oil and add air compressor lube oil.

I don't think that the wrong oil would, all of a sudden, make the compressor trip out on thermal overload, if that is what is happening.

You say it trips out. What exactly trips out? Is it the thermal cut out on the compressor or compressor motor, or the breaker?

How long have you been trying to run the compressor with motor oil in it? If it's been a while, that may be a contributing factor.

How about reading why air compressors pop breakers - if that's what's happening? That page is linked from the troubleshooting section.

Check the things referred to on that page, and then add a comment here with your findings if the compressor problem persists.

Cheers,

Bill

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