Thread: Air compressor drive problem

How old and what make is it? They do need to be properly serviced every year or so. The manufacturer should be able to help you out. Only other thing I can think of is that the cylinders/pistons may need to be lubed.

How weird! My compressor has also been going nuts lately, but not the same as yours. I don't think phase of the moon is involved.

Mine is smaller, and doesn't exhibit belt chatter (I think); but it does trip the breaker. Which was a major PITA, because it was temporarily on the same circuit as my computer. I learned this after the UPS had timed out. I was only trying out a new air tool, and set the whole thing aside for a while; so I haven't probed very deep.

With or without belt chatter, tripping the breaker suggests to me that it needs a new capacitor, and/or repair of the centrifugal switch.

V-belts can generally tolerate about 5 degrees mis-alignment (e.g. for 1/4-turn drives), so I don't think that's an issue - yours are about half that.

Cheers,
Joe

Sounds like the no load valve is faulty, i.e. the pressure is not bleading off on shut down and when you start it up again there is too much load so it trips the breaker. The belt chatter is the belts slipping as the compressor can't turn.

thanks for the suggestions chaps

the compressor is about 3 years old (has been in use about 30hrs in that 3 years, mind!). the pump has a sump that ive kept full with a compressor oil (dunno the weight, came recommended though) made by scorpion. im not keen on sending it back to the manufacturer, firstly cos i wouldnt have a clue as to where to send it i bought it from ebay secondly id rather exhaust the options im capable of trying before sending it away for fixing

thanks joe, capacitors are worth testing hey, ill do that tomoz

china, theres a pressure relief valve near the regulators, seems to be still working as when i rotate the pump by hand i can hear/feel air being released. is that what you mean or is it something else you're referring to?

ive got a quick pic of it;



its a TWM ACBD3350W (kinda stupid part number, but there it is)

Originally Posted by jardyDIY

china, theres a pressure relief valve near the regulators, seems to be still working as when i rotate the pump by hand i can hear/feel air being released. is that what you mean or is it something else you're referring to?

I don't think that is what China is referring to????
Normally when the compressor reaches max pressure and the pump/motor shuts off, you hear a sudden burst of air (it's under a bit of pressure) from around the pressure switch area. Do you hear this sudden rush of air when the motor stops running?

ive pulled it all apart today to suss what china meant

there's a check valve that runs out from the hot line between the tank and the pump, the one that i can feel releases pressure for a second or two when i turn it off, and when i turn the pump by hand (low enough pressure for the check valve not to close yet?) but it does it every time i stop it, whatever pressure the tank might be (ie max pressure or lower)

i removed that and dissembled the pressure switch, didnt find anything untoward, but did clean the check valve (dont think it needed it but did it anyway) and so far as i can tell it works alright. ive put it all back together, and the problem still exists :\

i thought perhaps the belts were wearing at different rates causing a bit of imbalance (one stretched more than the other maybe i dunno) so i removed one of the belts and ran it with a single one, the problem still happened but after trying a few times in a row, it operated normally. if i stopped it, waited 5ish seconds and started it again, itd be fine each time i started. but if i left it for a bit longer, itd happen again. from this short test it seems it only likes to work when the belt is warm?

ill mess about with it some more and try again with the other belt only, then both of them. if problems persist ill go and get fresh belts and see if that works. sitting around unused for most of the 3 years ive had it might have done them bad... cars arent nearly that fussy with em, might be why i didnt think of this before heh

thanks for the suggestions ill update with progress or hopefully solution, might help someone else thats frustrated with their bloody compressor

edit got one fresh belt, but bursons didnt have two nor did the other auto places near me so i need to wait till monday till another one comes in

This could also be an electrical. Have you had a careful look over the motor and associated circuitry? It could be an issue with the brushes, or the contacts. If you have a crack in a brush or some corrosion on the contacts then that would explain the issues you are having. It may be that when the humidity is higher or it is cooler that the problem comes out but when it is warmer and dryer the resistance is less and hence it doesn't manifest.

I'd check over the circuitry very carefully. If you aren't confident with that get an electrician to check it over. If your breaker is arcing out there is likely an earth leakage somewhere. This can be quite dangerous you don't want a fire or an electrocution.

When you refer to "belt chatter" do you mean that the belt moves forward and backward a short distance but the motor does not start? This is most likely due to the centrifugal starter switch contacts inside the motor being burnt and not properly connecting in the starter winding and start capacitor. Could also be the start capacitor itself, but I suspect the switch contacts as you claim it is intermitent (80%). The cap would be more like permanent.

As previously mentioned the no load valve is integral to the pressure switch and connects to the high pressure inlet to the tank by a narrow bore copper line. There should be a check valve at the point where pump manifold connects to the tank. The no load valve opens momentarily each time the motor is stopped by the pressure switch or on/off plunger switch on top of pressure switch. When it opens it bleeds the high pressure air in the pump manifold to atmosphere so the motor can start to turn with a modest load, while the check valve at the tank input prevents the tank HP air from bleeding back into the manifold.

If there is a fault in the supply line check valve, HP tank air could bleed back into the manifold pressurising it and making starting difficult. This could cause the motor to stall and create similar symptoms. easiest check would be to pressurise the tank and then open the fine bore pipe connection at the pressure switch. If air continues to bleed after the normal short burst, it has to be getting past the inlet check valve .

Disregard Heraldic's comments about brushes, the motor is an induction motor and does not have them. I assume that you had removed the fan shroud when the photo's were taken, the fan blades should not normally be exposed. The motor also looks a bit small for a 4HP unit.

Take the single belt from Bursons back if you have not used it, and get a pair from someone with a reasonable stock level. Multiple belts used in parallel must be length matched. Belt lengths have a tolerence of about 5mm, so you might need to check a few belts to get a pair that are within a mil or so. Not much chance of getting a matched pair if they have a couple in stock, particularly if the are sourced into the store a few months apart.

Originally Posted by Horaldic

This could also be an electrical. Have you had a careful look over the motor and associated circuitry?

i havent cracked open the motor as id need to remove the pulley, ive the tools and am capable of it but i was hoping to avoid it. good thing to keep in mind though, ill have a good look inside if i gotta
aside from inside the motor, ive poked around the with wiring up top (where the caps sit and the middle bit where the power line goes) and it looks near immaculate. its kept dry and out of wind etc though so id hope that it is quite clean inside heh. i also checked out the pressure switch when i dissembled it all, again everything inside looked fine, no real discolouration or greeny bits etc

Originally Posted by malb

When you refer to "belt chatter" do you mean that the belt moves forward and backward a short distance but the motor does not start?

sorry, im not great at explaining things (frustrating when people are trying to help, i know heh) by chatter i mean the belt is slipping. it'll slip and grab then slip and grab very quickly, which makes the whole compressor shake quite violently, and naturally makes a nasty noise id describe as chatter. the motor still runs at id guess roughly normal speed, just the belt is slapping around and everythings shaking quite nastily.
ive run the motor without belts a few times (ie start up, let run for a few seconds, shut it off, leave it for a bit then do it again) to see if span freely and it ran beautifully, i wouldnt have thought loading it would influence the effect of the potential motor problems you mentioned, but if you think it will, ill pull it apart and see what i can see

Originally Posted by malb

As previously mentioned the no load valve is integral to the pressure switch and connects to the high pressure inlet to the tank by a narrow bore copper line. There should be a check valve at the point where pump manifold connects to the tank. The no load valve opens momentarily each time the motor is stopped by the pressure switch or on/off plunger switch on top of pressure switch. When it opens it bleeds the high pressure air in the pump manifold to atmosphere so the motor can start to turn with a modest load, while the check valve at the tank input prevents the tank HP air from bleeding back into the manifold.

If there is a fault in the supply line check valve, HP tank air could bleed back into the manifold pressurising it and making starting difficult. This could cause the motor to stall and create similar symptoms. easiest check would be to pressurise the tank and then open the fine bore pipe connection at the pressure switch. If air continues to bleed after the normal short burst, it has to be getting past the inlet check valve

great, going by that description the check valve ive mentioned is what you're talking about there. i was poking about with the mechanism that controls that valve and it functioned like it should - when the pressure switch is up (compressor on) it'll break contact with a little plastic bung that normally holds the valve open, so when compressor is on, the valve shuts and remains shut, until the pressure switch is knocked down (by me, when i turn it off) in which case it'll make the check valve open, which will allow air to bleed off from the hot line when the pump stops (between pump and tank), just as you've described
seems to work fine when i was messin about with it, but i will try that test tomorrow.

Originally Posted by malb

Disregard Heraldic's comments about brushes, the motor is an induction motor and does not have them. I assume that you had removed the fan shroud when the photo's were taken, the fan blades should not normally be exposed. The motor also looks a bit small for a 4HP unit.

I did remove the shroud cos it was a little bent and i was worried it was fouling the fan, the fan has a few light gouges in it but still works good its back on now, directing air like it should be. as mentioned its only claimed 4hp, i certainly wouldnt defend that claim it wouldnt surprise me if they were stretching the truth a little, i dont mind though it drives my tools nicely. well, did drive my tools nicely

Originally Posted by malb

Take the single belt from Bursons back if you have not used it, and get a pair from someone with a reasonable stock level. Multiple belts used in parallel must be length matched. Belt lengths have a tolerence of about 5mm, so you might need to check a few belts to get a pair that are within a mil or so. Not much chance of getting a matched pair if they have a couple in stock, particularly if the are sourced into the store a few months apart.

i didnt know that, ill look into it the bursons i go to regularly (a few times a week usually) are a competent bunch, they do more to help me than any retail person ive ever known, when i gave them the sample belt they measured it to the millimeter and said they only had one to match it, the others were at least 5 or so mm off. ill drop in monday see if their supplier can sort me out with what i need. if not ive got another place i can try for specific belts

thanks heaps for the suggestions chaps, always good having things to try before giving up

Sorry for delay in replying, found your post last night but had to get into shed and take some photos today to clarify things. I have included a couple of photos of my unit with a similar tank, true 3HP output power Chinese iron motor, and a twin cylinder 17CFM free air delivery pump.

From your quote 3, it seems that you are confusing the no load valve in the pressure switch with the check valve at the point where the pump outlet manifold enters the tank. I have attached a close up photo of this valve in my unit , plus a general arrangement showing its position between the motor and pump.The pump manifold has the spiral cooler on it, and the no load bleed line is the thin copper line that connects to the check valve with an elbow.

I have also drawn a rough schematic of the air side of the compressor, (with the pump manifold shown in blue and the no load bleed line in red ) to try and explain the system. From the schematic, the check valve is located at the air entry to the tank, and allows flow only from the manifold to the tank. While the motor is running, the pressure in the manifold and bleed line will be greater than that in the tank, and will open the the check valve to force air into the thank.

When the tank pressure reaches the threshold for the pressure switch (or you turn the comp off at the pressure switch), the switch will disconnect the motor power and simultaneously open the no load bleed valve in the switch. This will allow the high pressure in the manifold system to bleed via the bleed line and no load valve, reducing the pressure in these lines to atmospheric pressure but the tank check valve prevents air flowing from the tank back to the manifold. Then when the tank pressure drops due to air being used, the motor can start with only mechanical friction in the pump and belt drive system as a load as it takes about 10 revolutions for the compressor (about a second) to develop a significant pressure load in the manifold system and load the motor.

For the motor to start but not fully drive the belt, either you have a severe case of Chines beltittis (crappy belts), very poor belt tension, undue friction in the pump, or the tank check valve is leaking back into the manifold and recharging it, stalling the compressor when the motor starts.

Hope this makes sense.

Re replacement belts, a matched pair 5 mm shorter than the ones removed should be OK, 5mm longer may be OK if you have adjustment capability to absorb the extra length. I would prefer to go to the shorter unit on the off chance that you have used all the adjustment available in the motor base already.

thanks for that you're right i am getting those two valves muddled up. thanks for sorting that out for me, i think i've got my head around it now

i hit bursons again today and they got me a matched pair of belts (was actually 3 belts in succession lucky)

put em on, tightened em up good, lined the pulleys up very closely, started up fine the first few goes but then went on to chatter once more

as you've rightly suggested itd appear the motor is struggling against the pump for some reason

ive pulled the check valve on the tank off and apart, but before that i removed the manifold line from the check valve to find it wasnt under pressure. the tank was only mildly pressurised cos the belts started chattering again, maybe 20psi

i removed and dissembled it completely and it looks fine inside. the little stopper (at the end of a spring) is made from a sort of urethane it looks like - quite soft. the mating surfaces of the stopper and its seat arent irregular and look nice and clean. other than that id say its alright. is there anything that could be wrong with it, that wouldnt be outwardly obvious?

which points the finger at the pump itself causing undue friction as you've mentioned. a complete stab in the dark but might be failure of those simple shim pieces they use as valves in the heads. out of interest i plugged the intake for each head seperately and rotated it by hand to find two of them seemed to draw in more air than the other

time to pull things apart again i spose

The "shim pieces" are called reed valves being similar to reeds in woodwind instruments.

My pump had a low oil run about 18months ago due to a slow oil leak developing in the threads of the sight guage supplied to check the oil level. Plastic sight gauge.

Stuffed the crank main bearings (chinese ball races) quite nicely but did not damage the big ends, conrods, gudgeons, pistons or bore. I stripped it down and took the crank and bearings to my friendly mower guy who pressed the bearings off and new Jap ones on for $30. Reassembled the unit and it works like a charm again, but I check oil level more often now.

there are a few mower/small engine mechanics around where i live. i didnt think to go to them for help with a compressor. im friendly with a well equipped engine rebuilder place near me too so shouldnt have too much drama getting help if the pump needs some professional attention

thanks for the suggestion i wouldnt have thought about mower places

ive been checking oil level every time i use it (which isnt often so its no real trouble to check that often) since a mates one died when we were using it

Alan, disconnect the power remove the belts disconect the one way valve and the no load valve then rotate the compressor via the flywheel by hand and see what the result is, with every thing disconected if it still jams up then the problem is the compressor itself