Air compressor questions

**nathanwhite** · 9th August 2012, 22:10

I don't think this is the right place exactly, but it seemed the best fitted.
I have recently come into possession of a second hand air compressor (mucho bling to Maha and Mom) and have a few questions seeing as this is the first I've had.

How hot is it supposed to get? Currently after a couple of minutes work the head is almost too hot to touch. I know its a head dispenser, but is this normal?
Is there supposed to be positive air pressure in the crankcase? There is a small hole in the yellow bit that is blowing air at me
How much time does a unit like the one pictured take to get up to ~50psi?

Picture

Ta.

**pete376403** · 9th August 2012, 22:19

No picture so not sure what you've got - compressing air does raise the temperature. Thats why turbos have intercoolers. My SuperCheap compressor gets hot enough that the pipe between the compressor and the tank melted a coiled plastic air hose that was touching it.

The crankcase venting system is pretty basic so yes it does seem like there's a stream of air coming out of the hole in the oil fller plug.

Takes a good three or four minutes to get up to full pressure (before the pressure switch cuts the motor.)

The flap valves in the head break occasionally

These things are built down to a price not up to a standard.

It's also worth draining the water from the tank from time to time (the tap underneath the tank)

**nathanwhite** · 10th August 2012, 08:37

Thanks,

Hmm, making a list broke my link it seems. Edited now.

Also does anything weird happen to thread tape when it gets to aforementioned temperatures? There's a leak in the connection of the head to the output pipe to the tank that I'm going to have to patch up

**Flip** · 10th August 2012, 09:52

PTFE tape will be fine.

Compressors do get very hot.

Is it an oil-less compressor? or does it have oil in the crankcase.

**tri boy** · 10th August 2012, 09:55

Originally Posted by nathanwhite

There's a leak in the connection of the head to the output pipe to the tank that I'm going to have to patch up

That will explain the slow pressure build up.
Some of these budget comps have a sealant on the fittings that need a bit of heat to break loose.
Thread tape is fine for the sealing duties, but a hydraulic locking sealant is also good.
The unit does get hot, and if it has an air leak, it is working twice as hard as needed.
Keep an eye/ear out for comp big end noise.
So lubricate with minimal oil, some with a grease.

**nathanwhite** · 10th August 2012, 10:22

Originally Posted by Flip

PTFE tape will be fine.

Compressors do get very hot.

Is it an oil-less compressor? or does it have oil in the crankcase.

Very definately a oil filled one.

Originally Posted by tri boy

That will explain the slow pressure build up.
Thread tape is fine for the sealing duties, but a hydraulic locking sealant is also good.

Brilliant, I'll pull it apart later on today and see how we go.

**Akzle** · 10th August 2012, 11:34

Originally Posted by nathanwhite

1)How hot is it supposed to get? Currently after a couple of minutes work the head is almost too hot to touch. I know its a head dispenser, but is this normal?

yes, single cylinders especially get quite warm. compressing air creates heat. you're compressing a lot of air.
the electric motor will have a fan at the arse of it, and that plastic cowling will help blow it over the cylinder's fins. don't take it off.

2)Is there supposed to be positive air pressure in the crankcase? There is a small hole in the yellow bit that is blowing air at me

i assume that's a slide check. slide it to cover the hole.

3)How much time does a unit like the one pictured take to get up to ~50psi?

it will run to (typically) 90psi. you can play with the little electric/pressure switchey bit to crank it as high as you like. bear in mind your receiver is probably only rated to 115psi. i keep mine at 110. (ingersoll-rand = qualities)
time? depends on air temp, pressure, humidity, how much is already in the tank, etc etc. if it's taking longer than 5 minutes running, something is probably wrong.

hints for owning a compressor:
keep in mind the duty cycle. it will not be apropriate to run a big syphon paint gun off this (get a 3 cylinder belt drive one

)
keep in mind your cfm or lpm (free air delivery) this can be tutu'd with connectors and stuff, but you generally won't get much more than the unit is rated for.
DRAIN THE FUCKING RECEIVER.
if there isn't a hole/bolt in the bottom to take out, take one out the top/end and get the water out of it. i dismantled a 20lt bunnings jobby and got 15lt of water out of it and the cnut wondered why it wasn't going to good for his painting.

- obviously, this is best done with the unit unplugged and nearly out of puff.

just in case you didn't know.
/$0.02

**Akzle** · 10th August 2012, 11:38

Originally Posted by Flip

Is it an oil-less compressor? or does it have oil in the crankcase.

jeez. who gives away oilless compressors? i want your friends...

pluus, aren't they normally of the centrifugal variety?

Originally Posted by tri boy

So lubricate with minimal oil, some with a grease.

errr.. oil. compressor grade oil. for pretty much any reciprocating compressor you can afford.

**bogan** · 10th August 2012, 12:08

yeh as akzle said, don't expect to paint bodywork with it, single cylinders running at their limit of cfm pass heaps of moisture through. Get them leaks sorted and it should be pretty handy though.

**nathanwhite** · 10th August 2012, 13:13

Originally Posted by Akzle

errr.. oil. compressor grade oil. for pretty much any reciprocating compressor you can afford.

Yep know that much at least

Originally Posted by bogan

yeh as akzle said, don't expect to paint bodywork with it, single cylinders running at their limit of cfm pass heaps of moisture through. Get them leaks sorted and it should be pretty handy though.

Not even small bodywork like bike panels?

that was one of the things I was really looking forward to

**bogan** · 10th August 2012, 13:42

Originally Posted by nathanwhite

Not even small bodywork like bike panels?

that was one of the things I was really looking forward to

Maybe if you get a decent water trap, and run low duty cycle.

**Akzle** · 10th August 2012, 14:38

Originally Posted by nathanwhite

Not even small bodywork like bike panels?

that was one of the things I was really looking forward to

get a gravity feed gun with a <1mm tip, should see you right. find a gun with the lowest FAD requirement you can, run it as lower pressure as you can so the motor isn't running continually. (bunnings sell "touch up" guns suitable for cheap enough, makes a long job of it though)

and yes get an inline water trap, personally i'd stick it at the tank so you're not getting wet through your hoses.
also, if the hoses have been used for tools they may have had tooling oil through them. this is not good for paint. (buy clean hoses)

**tri boy** · 10th August 2012, 14:54

Originally Posted by Akzle

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errr.. oil. compressor grade oil. for pretty much any reciprocating compressor you can afford.

Not all compressors, (although this one does indeed use oil),
but hey, what would I know, I only work for one of NZs bigger comp importers/onsellers

Ever seen a dairy shed oiless unit, that purges the milk lines? They can't use oil, (or even food grade grease) instead it uses special big end brgs, and teflon rings, but I digress...........