I've got a Puma pk5030v compressor which has started to trip the breaker when it tries to start up with pressure in the tank. The motor tries to turn the pump, but it can't get it moving and then trips the breaker. When I expel all the air and let it start up with an empty tank, it will kick on and run fine until it turns off at 150psi, but then when it tries to kick back on when the pressure falls to around 100psi, it can't get the pump moving. I'm assuming that there must be pressure built up in the pistons, so most compressors you replace the 'unloader' valve and that's the problem ... however, this compressor uses what they call a 'check' valve that screws into the tank, and there doesn't seem to be any 'unloading' port or hole on that valve. I also don't hear any kind of air released when the compressor kicks off like I do on other compressors. Has anyone dealt with this kind of setup? I have replaced the 'check' valve; however, I used one made by Conrader (https://www.amazon.com/gp/product/B003H7ITEW/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1) that is supposed to be the same as the OEM and the compressor is doing the same thing. I've got the OEM one ordered (https://www.ebay.com/itm/CV1212-PUM...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649) just in case they are different, but they don't seem to be. Oh, and I did replace the start capacitor just in case, but that wasn't the problem either.. anyone have any experience with this?
Compressor problem - tripping breaker when trying to start under pressure
- Thread starter bigjws
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MEP001
Well-known member
The compressor should be able to start against the pressure, but it's really hard on the start components and will shorten their life. Yours is probably failing from not having the pressure relief parts to prevent this. My bet is that you're going to end up replacing the motor. You might get some more life out of it if you replace the motor pulley with a smaller one, as long as you don't reduce the recovery rate so much that you run out of air.
You should have a relief line going from the tank check valve to the unloader on the pressure switch. If the there is a problem with the pressure switch unloader the air compressor may have a hard time starting. It might behoove you to just change out the pressure switch if your not hearing the pressure switch unloading after the air compressor stops. If that's not the problem try replacing the start switch in the back of the motor.
So Randy, you're saying the pressure switch may have the 'unloading' valve attached to it? I've always seen it at the tank where the check valve is, but I figured there should be one somewhere on the compressor. I'll take a look and see what there is - would the pressure switch actually contain the unloader valve, or would it be 2 separate pieces (switch and valve)?
Yes the pressure switch should have an unloader on the switch. The unloader is on the left side of pressure switch in the picture. Its got a port on it so you can connect tubing to it that runs down to the tank check valve. When the air compressor stops it relieves the pressure in the line from the air compressor pump to the tank check.
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MEP001
Well-known member
It should have one. A compressor that size would most definitely have come with one. It's possible it got replaced with one without it, just like the tank check valve got replaced with one that doesn't have a threaded port for the tubing that goes to the switch. Or it's got a relief valve and it's just not connected to anything. Either way, IMO the motor is now the problem.
There is also a device called a "Load Genie Check valve" https://mastertoolrepair.com/s10-style-load-genie-check-valves-s10-style-p-1418.html I've used them on a few air compressors with good results. Try this test. Run the air compressor up to full pressure, when it stops loosen the line from the pump to the tank, to relieve all the pressure from the pump, lower the pressure so the compressor starts. If it starts with no problem you've got a problem with the start switch unloader, replace the switch.
That's basically what I did when I let all the air out of the tank/pump, then started it up .. it started just fine with no pressure, so I think having pressure in the pump is what is stopping the motor. I agree with MEP that the motor should get it going anyway (it's been running this way for years and I can't think of a time that I've heard the air purge out) so I think the motor is getting weak, but I'm probably going to try to figure out the unloader part first -- I'm thinking without startup pressure I may get some more life out of the motor.
I'm thinking this has something to do with it. It does have a hose running from the check valve to the pressure switch; however, it's a 'hose'...the copper tubing has been replaced with hp hose, so the compression fitting that comes with the pressure switch has been replaced. I'm wondering if the 'unloader' part was accidently removed with the compression fitting, and it's just run without it for all these years. I'll break it down tomorrow and see what I can tell..
This type of device is what I have on the main compressor at my other location, and is what I thought was the actual 'unloader' valve. If all else fails, I may just add one like this and make my own 'unloader' location.
If you relieve the pressure off the pump and the air compressor starts with no problem your problem is with the pressure switch. I use black 1/4" DOT brake line from the tank check valve to the pressure switch unloader. Over the years I've gotten a number of expensive air compressors for free that all they needed was a tank check valve or some TLC.
MEP001
Well-known member
Here's the parts breakdown if it helps:
Greg Pack
Wash Weenie
Good thread guys! My compressor is starting to act up and I don't know a lot about them
cantbreak80
Maybe I need new clubs
Air compressor unloader valve | the Workshop Compressor
theworkshopcompressor.com
Wanted to update - got the new pressure switch and that fixed the problem... I can now hear the air purging when the compressor cuts off. As MEP noted, the motor has probably been weakened since it's been running without unloading the air for years, but for now it seems to be working fine -- I'll try to remember to update when the motor actually fails in the future to see how much time I bought..
MEP001
Well-known member
That's not what the check valve in the tank is for, and he just said the pressure switch was bad and not relieving the pressure from the head. I just changed mine which was doing the same thing.
If the check valve is bad and the pressure switch is bad and not letting the pressure off the head it will usually trip out because most can’t start under load.
MEP001
Well-known member
The check valve in the tank only traps the pressure in the tank. If both the tank and switch are bad, there's still the same pressure trapped in the head. Again, he already said the switch was bad and he's changed it. If the check valve was also bad, the switch would now constantly purge air when the compressor isn't running.
I.B. Washincars
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Agreed...
