Cannot start up my compressor when there is air in the tank.

by Fred Holmes
(UK - Hartlepool)

Hi There,

I have a cheap 45 litre tank compressor.
When i use the compresser at the start of the day , it will not pump and buzzes for a few seconds , and blows the thermal trip , i then reset it , and same again, it will always do this when there is air in the reservoir.
If I bleed the air out all is well, and the pump fires up , charges up the reservoir , and then cuts off at 110psi. when pressure drops off , it kicks in again , and all is well, I only have a problem at the beginning of the day ?
Do you think it is the pressure switch leaching back into the pump, but very slowly... ?
Regards...Fred

fred@bayview.be






Bill says...

Hi Fred. When compressors have a hard time starting when there is pressure in the tank, I'd look to the unloader valve first.

Here's info on how Unloader Valves work.

Cheers,

Bill

Click here to read or post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Has Unloader Valve Issues.

Motor freezes temporarily

I have a Kobalt 1 1/2hp 17 gallon, 155 psi compressor that will build up pressure to the shut off point and when it tries to restart as pressure is used the motor locks up and just makes a humming noise until it trips the breaker. If you turn it off and leave it for awhile it will start up and do the same thing all over again. I have replaced the pressure switch and that didn't help.






Bill says...

G'day, and thanks for writing in.

When the compressor last built up pressure to the cut out pressure level, and the motor stopped, did you hear it unload?

My guess is that you have an unloader valve problem.

Cheers,

Bill

Click here to read or post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Has Unloader Valve Issues.

Compressor fails to cick in.

by Nabeel
(South Africa)

I bought a new non return valve but it might be falty, the compressor runs full with no problem and cuts out as normal, but when its time to cick in the motor labours and it fails to start, if i release the 6mm pipe that is atached to the non return valve and the cut out switch the compressor runs and if i dont do that i must wait until the air is completly run out, is it a falty non return valve or if not what might the problem be. (Please help!)






Bill says...

Hi Nabeel. Nice to hear from you.

No, it's not your return valve, I don't think. I believe your problem is with your Unloader Valve.

If your unloader valve isn't working, the motor may not have enough strength to start the compressor against the air pressure trapped over the piston.

Cheers,

Bill

Click here to post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Has Unloader Valve Issues.

motor starts or runs slowly

by johnnyh
(loudun, france)

hi,
i have a single phase motor, direct drive compressor that often, though not always, starts slowly or runs slowly for several seconds. eventually it picks up and runs fine but i have gone so far as to take the heads off the cylinders to check it is not a stuck valve or something causing the slow start. it used to run fine but was left unused for several years and now does this. i have wired the motor (plus it's start capacitor) directly without the pressure switch and it behaves the same so it's not the switch or, i think (due to head removal) any part of the pneumatics.
could it be the motor itself or it's capacitor?

_______________________________
Bill says...

Hello Johnny, it could be the motor, but I'm actually inclined to think that you might have extra load on startup, and that extra load may be caused by the compressor not unloading when it reaches cut out pressure and shuts off.

If you aren't sure what Unloading is, please read the page on this site, and make sure that you are getting unload each time the compressor shuts off.

Cheers,

Bill

Click here to read or post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Has Unloader Valve Issues.

Motor stalls when re-loading

Hi,

Our compressor fills to cut-off pressure, motor goes to idle then when ready for re-load motor immediately stalls.
Any idea's. Thanks!






Bill says...

Sounds like your unloader valve isn't.

Is it?

Cheers,

Bill

Click here to post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Has Unloader Valve Issues.

Oil type rotary screw unloader valve

this unit is a homan howden 2855 1265 and is only building about 40psi with discharge valve open. with it closed it will pump up to about 120 psi. at about 40psi the valve opens or closes i guess how ever you want to look at it.






Bill says...

Now you've gone and confused me? :-)

You say discharge valve...that's not the unloader valve.

The unloader valve is only supposed to open when the pressure switch toggles the compressor motor to off when the high pressure cut out level is reached.

If air is bleeding out of the unloader valve when the compressor is running, you either have a leaking check valve, or the unloader valve / pressure switch isn't working properly.

Good luck.

Bill

Click here to post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Has Unloader Valve Issues.

Air Compressor Stalls on startup

by KL
(Bay Area,CA)

My air compressor Central Pneumatic 2hp 8 gallon is having problem when it try to starts automatically.

The motor runs fine when its first started, and it builds pressure to its max cut off of 115psi. The problem occured when it tried to start automatically when the pressure goes low. When it attempts to start, the motor is having a hard time, it create this noisy popping sound like its going to die, and it will eventually die. It wont turn on if I turn on the switch. I found out that it will turn on again if I press the reset button on the side.

I was wondering if it has do with my garage's electrical supply, if I have enough electricity to power the compressor.

Thanks.

___________________
Bill says...

KL, it might be the power supply, but I suspect from the symptoms it's more than likely it's your unloader valve that's not working.

Cheers,

Bill

Click here to read or post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Has Unloader Valve Issues.