Compressor Intermittent Fault Any Ideas?

[geoffsurf]

Some of you may remember from my previous post that I had an intermittent problem with my compressor. Sometimes when it would start it would begin to run, but then slowly stall before getting up to running speed. I would have to immediately turn it off else it would trip the fuse box switch.

I took the motor off and took it to a local electric motor repair shop. They said that the capacitor was breaking down under load and also changed the bearings on it. I refitted the motor and it started up great and was a lot quiter with the new bearings.

A few days later I used the compressor during the day, left it full for a couple of hours while I went out, came home, and used it, it then tried to start up but stalled slowly just as before. I have been using the copressor for the last few days, it has mostly been good. However, today it has stalled and tripped the fuse box a number of times.

I am not sure what this fault could be, I don't really want to take the electric motor off again because the bolts are fiddely and it seems to be lined up correctly with the pump now. Could it be that the brand new capacitor has broken down again?

When it had the problem before I took the motor to be repaired, I would check the pump and each time it seemed free. The air also seems to be dumping when the compressor cuts out or the switch is turned off and on. However, when it won't start up properly and I completely drain the tank it will usually then start.

This problem is starting to get annoying, has anyone any ideas what it could be?

 

[the snooper]

some compressors have an easy start valve that only seals when the motor is up to speed does yours have one and is it faulty
it sounds like it should

 

[rtbcomp]

You say the air dumps OK when it switches off. Do you know if it dumps OK everytime it switches off, or perhaps it doesn't dump occasionally and that's when it won't start up again?

I had a problem with a brand new Clarke where there was a bit of debris in the relief valve in the pressure switch which caused a similar problem.

 

[awemawson]

My hydrovane had the pressure switch plumbed in using a one way valve - only ever worked as the valve had a bit of leakage, now replaced by a straight nipple. And this came from someone setting themselves up as a compressor specialist !!!!

 

[geoffsurf]

Hi thanks for the fast replies. I should have mentioned this is a Taskmaster 160ltr, 3 Hp, single phase compressor. Here is the link to the thread with some pictures if it helps identify:

http://www.mig-welding.co.uk/forum/showthread.php?t=21034


the snooper - Not sure if mine has one of these valves you are talking about. Maybe you can tell from the pictures in the link above? I am guessing that this would be like a automatic drain filter and would leak air untill enough pressure builds?

rtbcomp - I think it is dumping air each time fine. Because when the compressor tries to run but then stalls on start up, I quickly turn it off and it hisses. I then turn it on and off each time hoping that it will run but it just keeps trying to run and then stalls (I repeat this a few times). However, each time it hisses quite loud and dumps the air. The other day I was turning it off and on trying to get it to run and one time it didn't dump the air, the compressor then wouldn't even try and start as there was too much compression, this has only happened once though and probably caused by trying to turn it on and off too quickly.

awemawson - The previous owner didn't seem to have problems with it really. I am not sure how I would check the pressure switch valve, but it doesn't seem to have been tampered with.

 

[piman]

Hello Geoff,

does the motor have an inertia switch for the capacitor, there could be a poor contact there? Is it belt or direct drive by the way?

I wouldn't have thought that the capacitor would have failed so quickly, but it's worth checking the connections in side the terminal box. Any burnt smell when you open the box is a bad sign also.

Alec

 

[the snooper]

here is a picture of the valve note that the arrow points to a nut that moves in and out slightly.
this valve releases air until sufficient air is produced to close it

 

[geoffsurf]

Piman - Hi Alec, I am not sure if the compressor has an inertia switch for the capacitor, I am not sure what one is? There doesn't seem to be a physical switch anywhere around it if that is what you mean. I opened the cover where the capacitor is wired to the motor and it all seems fine with good connections. It is a belt drive compressor.

the snooper - thanks for the picture, no I don't seem to have one of those on my compressor.

 

[brightspark]

Piman - Hi Alec, I am not sure if the compressor has an inertia switch for the capacitor, I am not sure what one is? There doesn't seem to be a physical switch anywhere around it if that is what you mean. I opened the cover where the capacitor is wired to the motor and it all seems fine with good connections. It is a belt drive compressor.

the snooper - thanks for the picture, no I don't seem to have one of those on my compressor.

what he means is some motors have a centrifugal switch in the starting windings on the shaft inside motor. it opens circuit when up 2 speed

 

[geoffsurf]

Ok, not really sure about that. When I took the motor into be fixed they said that the internals of that motor were good and would go on for many years.

 

[eil]

A problem I have encountered, and this is after a motor having been returned from a re-winds shop, is as already pointed out by the two sparks already, was the centrifugal switch on the motor ,now the sneaky problem I found was that it started with no load like yours does, but didn't afterwards, the reason was when I removed the back cover off the motor and the cooling fan I could see that only one of the two contacts was making at the centrifugal switch while at rest but there was a gap on the second contact so it behaved when there was no load at all on the motor but would stall when starting against the smallest of pressure.

 

[drivewasher]

You say it hisses every time you switch the switch. It should only hiss once when you or the switch stops it. this is the underloader dropping air out of the pump high pressure side so as to allow the motor to start the next time its required without any load on it.

Looking at your compressor in the link, by the side of the pump is a kinda elbow union with a fine tube that goes to the switch. This is the tube the switch opens to dump the air on stopping. That union encorporates a crude one way valve to stop the tank filling the high pressure side of the pump back up when its stopped. If it does cos its faulty the motor wont start.

With the tank COMPLETLY EMPTY OF AIR (very inportant for safety) and the mains isolated remove the big nut on top of the elbowed union it has a rubber disc in it, clean it out and fit a new rubber, you can try turning it over but if its damaged or split it needs a new un.

The rubber disc is forced against its seat by the pressure of air in the tank this stops air going back into the pump and switch, when motor starts up again the pressure from the pump pushes the rubber disc off its seat allowing air into the tank when motor stops the switch once again dumps the air trapped between the elbow and the switch/pump.

Oh and i take it you always stop the compressor by its own swith and not with the mains isolator or plug/switch or the underloader wont dump the trapped air

 

[geoffsurf]

Right. I wanted a friend to give me a hand when I took the valve off the compressor, just in case something went wrong.

Yesterday we took off the one way valve on the tank that comes from the pump. It all seemed okay, the rubber disc was ok. We also checked the tube that runs from the one way valve to the pressure switch to dump the pressure in the pipe between the pump and receiver.

The motor ran fine when it came back from the motor shop, so I didn't think it was a loose connection inside the motor. The compressor will start up for a second time if you drain the air immediately with an air tool. If you leave the compressor for any lenght of time with the tank full, the next time it goes to restart, it will not.

Still really stuck as to what the problem could be. Any more ideas?

 

[eil]

Start again by going through things methodically, with no pressure in the tank and with the drain tap open, disconnect from the mains, slacken the motor and take the belt off, check that the compressor turns freely if it does replace the belt and adjust then mains back on switch on at the pressure switch and let it build up pressure to about 30psi, then switch off at the pressure switch and listen for the pressure unloading under the pressure switch it should as you know hiss until there is no pressure left in the compressor discharge line, if it does this OK, then switch the compressor back on at the pressure switch, it should start up. If it doesn't and hums then switch off at the pressure switch again, you shouldn't get a hiss from it unloading this time as there shouldn't be any pressure in the line, as it should have completely unloaded the first time. if it tries to start and stalls then you will get some hissing from the switch but not as much as it did when unloading the first time ,if this proves the case, then disconnect from the mains again and undo the belts once again and try and turn the compressor by hand as you did before and see if its any different to what it was when you first tried it when the tank was completely empty. See how you get on up to there.

 

[the snooper]

i would be tempted to run the compressor switch of and then slacken the nut on the delivery pipe you should be able to undo the pipe and no air should escape that will confirm if the unloading valve is working correctly or not

 

[eil]

i would be tempted to run the compressor switch of and then slacken the nut on the delivery pipe you should be able to undo the pipe and no air should escape that will confirm if the unloading valve is working correctly or not

That was going to be the next step, thought i had written enough to start with

 

[the snooper]

it can only be either not unloading or the motor at fault becasue it starts when empty there is nothing else really

 

[eil]

Geoff, after posting two threads you are still having problems with your compressor it must be doing your head in by now, disregard my previous long winded post about going through things methodically from the start, as has been pointed out its not unloading or the motor is at fault.

 

[geoffsurf]

Yes it is definately doing my head in. It is still very much an intermittent fault. I turn it on when it is empty and it starts up fine and cuts out at 150psi, I use an air tool and at 110psi it kicks back in fine. Other times it stalls when trying to restart, I then have to drain the tank to about 20-30psi before it will start up without stalling. When I say it is stalling, it always tries to start up and spins the pump about one and a half turns before it stalls. I never just hums without turning.

The thing that makes it confusing is when I took the motor to the repair shop they said the capacitor was breaking down under load and so they replaced it. I didn't use the compressor much for the first weeks or so but it seemed to start almost every time fine. Then gradually it has got worse and worse until now it starts up about only 30% of the time.

There isn't really any compressed air companies around here so there is no one I can take it to. Also getting the motor checked, bearings replaced, and capacitor replaced cost quite a bit...

I will try taking the cooling fan guard off tomorrow and when it stalls I will check whether there is pressure at the pump. Before I took the motor to be repaired the pump was free even when the compressor stalled. The only other thing I can think of is that the spring isn't good enough on the one way valve and as the pump starts to pump air into tube and receiver, it opens the valve too early and the full tank pressure hits the pump too early?

 

[eil]

They put in a new capacitor when they replaced the defective one I take it, how many capacitors does the motor have ?.