Compressor problem

[BogMonster]

I've got a cheap-ish Draper 25L 8 bar 2hp direct drive compressor, cost a couple of hundred quid the best part of ten years ago now. It's not had a lot of use, occasional for air tools, cleaning and tyre inflation, but it's been abused a couple of times in my old job when a portable air source was needed away from the garage compressor and it got overheated at one stage just through continuous use - the mechanics were overhauling a big marine diesel on board a boat and needed a lot of compressed air for blowing everything out.

Since that (about 3-4 years ago) it's been getting progressively "stickier" with starting if it hasn't been run for a while, especially in colder winter weather. The motor will kick in and do half a dozen compression strokes over about ten seconds and then trip out its thermal cutout. Resetting it and then cycling it off and on a few times with the switch on the compressor (to release the air pressure in the circuit) eventually gets it going and once off it runs normally and charges the receiver at about the same speed it always has. Once it's done a cycle, it works fine for the rest of the session and comes on normally, but leave it to cool off for a few hours and it goes back to semi-seized state again.

One day I'll get around to buying a new one, but at the moment it might lead to domestic discontent (as I will get a £500 plus 3hp semi pro model with a big receiver next time around) and so I wondered what the problem is likely to be and whether anything can be done to fix it or extend its life, or whether I may as well just keep using it till it dies (which may be another year or two as I don't use it a lot).

It seems like it is partly seized, but never having been into the guts of one I don't know what is inside to seize up, I assume they are basically like the piston and valve arrangement in an engine but not too sure.

It also produces a lot of oil mist into the air in the receiver, it is permanently plumbed into a long extension airline and when you take the airline off the quick release fitting on the end of the receiver, you get quite a spray of oil and when I recently drained it I made a hell of a mess on the floor - mostly oil rather than water. Oil level in the unit itself is fine though has been topped up from time to time.

Any thoughts on possible causes or repair solutions please?

Ta

[CwazyWabbit]

The valves in these things are usually just pieces of spring steel and usually have little go wrong with them other than going rusty causing them not to seal, doesn't sound like that is happening so you can probably rule that out.

I'd be tempted to seperate motor and pump (I assume this isn't a belt drive) and see if the motor is stiff to turn by hand, in my experience the motor should spin very easily by hand, if it does strip the pump, if it doesn't strip the motor. The motor bearings may be knackered but I should think they will be easy to replace, anything else in the motor is probably not diy.

The pump will be simple to strip for someone like you, check the bearings and the state of the piston.

One last thought is the motor may have a centrifugal switch inside it, if it does it would be worth checking that it switches easily and the grease on it hasn't gone hard.

[pete3000]

I'd go with the motor bearings as well. I had one of these dd draper units apart a while back, it wasn't pleasant. The pump will sort of seperate from the motor, but he motor is actually part of the casting, and all alluminium. I tried to pull the ally crank and fan off the motor to look at the bearings and ended up trashing the lot.

[simonr]

First thing I would look at is the motor starter capacitor! Usually easy to get at and easy to replace. The capacitance value is not that critical - just replace it with one of similar physical size from another motor.

They have a finite life and the symptoms of failure (other than the capacitor itself exploding which happens sometimes) are difficult motor startup / low starting torque.

I suspect it may be a combination of needing some mechanical attention and the Capacitor. Unfortunately, high starting torque requirement shortens the life of the capacitor - so one may cause the other.

Si

[BogMonster]

The thing is, once it's been running for 30 sec it starts/stops as well as it always did, surely any of the above are likely to be f'ed all the time?

I'm loathe to pull it to bits as at the moment everything is airtight so it holds air for weeks, and I know from experience that once you rip something like that to bits it can be hard to get rid of all the tiddly leaks that lose air over a period of a couple of days.

I'll have a poke at it on the weekend anyway, ta

[simonr]

I'm loathe to pull it to bits as at the moment

You've got two choices! Pull it apart or live with it.

Si

[CwazyWabbit]

To be honest all the bits that involve it leaking over a few days will be after the one way valve on the tank and you don't need to disturb that, so pull it apart, you know you want to

You'd be surprised how different things will work with a bit of heat in them, btw just as a quick check is the motor actually warm to touch when the thermal cut out trips? Always a chance that is buggered and is tripping too soon.

[BogMonster]

You'd be surprised how different things will work with a bit of heat in them, btw just as a quick check is the motor actually warm to touch when the thermal cut out trips? Always a chance that is buggered and is tripping too soon.

The lights dim noticeably when it's trying to start and stay dim until the trip goes so while I haven't tried it, I think it's genuinely warm judging by the amount of electricity it seems to be absorbing

Si, I meant I was loathe to pull the airy bits to bits (erm ... sort of makes sense!). I'll check out the electrics and the bearings etc on the weekend.

[BogMonster]

The old one was definitely knackered dear, put the rolling pin down

I took the plunge and now have a shiny new one which is, to say the least, 'a bit of an upgrade'

AIE HW16, 150psi, 150L receiver and 3hp single phase motor, 16cfm displacement and 10.6cfm continuous FAD at 100psi. I looked at a few 3hp models inc Sealey and Clarke but eventually decided it was worth a couple of hundred extra to get something that would see out my days of wanting to wave spanners.

You can see the difference between a proper bit of kit and a toy, just the industrial motor on this is bigger than the whole motor and compressor unit on the old 2hp Draper! One of the air filters got damaged in transit, but easy enough to fix. I now have to finish rewiring the garage in properly, as they recommend a 30amp supply...

[landroversforever]

That does look nice!!