Thread: Care of compressor

Don't worry about the inside, they all end up a bit rusty like that.

When I started as a part time tech studies maintenance man for my son's college, they asked me to look at the compressor as is was constantly cycling! You guessed it! It hadn't been drained ever! This was a huge receiver! 2' Dia X 7' long! 100s of litres later!

Tankstand, I hope you don't mind my intrusion on your thread, however I too have a compressor maintenance question.

I recently acquired an old (1982) Atlas Copco direct drive compressor. It runs fine and does the job however I notice the oil in the window is very discoloured and could do with a change.

What oil should I use?

Thanks Tankstand. I'll just be more vigilant from now on.

Originally Posted by hitch

Tankstand, I hope you don't mind my intrusion on your thread, however I too have a compressor maintenance question.

Well, it is Mychael's thread!

Originally Posted by hitch

I recently acquired an old (1982) Atlas Copco direct drive compressor. It runs fine and does the job however I notice the oil in the window is very discoloured and could do with a change.

What oil should I use?

Sorry, I wouldn't know. It is often a light weight oil. I would not like to hazard a guess incase we damage the unit.

I'm thinking you could probably contact the service department of one of the larger manafactures. There must be places that service these things.Ask them what they use.

Or maybe try an engineering supply store that sells parts as well as tools.

Originally Posted by hitch

Tankstand, I hope you don't mind my intrusion on your thread, however I too have a compressor maintenance question.

I recently acquired an old (1982) Atlas Copco direct drive compressor. It runs fine and does the job however I notice the oil in the window is very discoloured and could do with a change.

What oil should I use?

******************
G'Day Hitch & Mychael,
Just use standard multigrade engine oil with older specs nothing fancy; but don't over fill it.
Depending on your use and the ambient environment it should be changed every 12-24 months;
though draining of the pressure vessel should be monthly for regular use.
Also Please, treat air compressors and compressed air with a lot of respect and remember that a cubic inch of compressed air at 100psi expands to a cubic yard [or cubic metre] at normal atmospheric pressure.
Cheers, Crowie

Thanks to you all for your responses and advice.

I will use the 30/40 multigrade that I have at hand.

Regards

Ian

I just recently purchased a new belt drive compressor and it specified ISO 68 oil.

Originally Posted by crowie

Also Please,[/U][/B] treat air compressors and compressed air with a lot of respect and remember that a cubic inch of compressed air at 100psi expands to a cubic yard [or cubic metre] at normal atmospheric pressure.

I don't know where this comes from.

According to Boyle's Law, P1 x V1 = P2 x V2

P1 = 100 psi
V1 = 1 cu in
P2 = 15 psi (Atmospheric pressure)

Therefore V2 is ~7 cu in.

Where as one cubic yard = 36 x 36 x 36 = 46656 cu in and one cubic metre = 62099 cu in.

Working it the other way, a cubic yard of air at Atmospheric Pressure has a volume of about 7000 cu in at 100 psi.

Even a cu ft of air at 100 psi only expands to ~7 cu ft of air at atmospheric pressure, this is equal to about 1/4 cubic yard.

All that aside I still agree about being careful.

Originally Posted by BobL

P2 = 15 psi (Atmospheric pressure)
.

small point but atmospheric is 0psig unless your 100psi is registered in absolute and not guage which is very unlikely. Since the expression falls apart, your starting value is 114.5 not 100.

Originally Posted by bonox

small point but atmospheric is 0psig unless your 100psi is registered in absolute and not guage which is very unlikely. Since the expression falls apart, your starting value is 114.5 not 100.

Yep I agree, but since atmospheric pressure cannot be zero (otherwise we'd all be dead) then its

P1 = ~114 psi
V1 = 1 cu in
P2 = ~14 psi
V2 = ~8 cuin , still a long way from 46656 cu in

Just to continue along this tangent .... it's not really the change in volume that causes the problems, it's the velocity of the change.

Originally Posted by Vernonv

Just to continue along this tangent .... it's not really the change in volume that causes the problems, it's the velocity of the change.

perhaps - might depend on the problem. Chernobyl was a problem of slow velocity, big change in volume after all....

Hi All,

"discoloured" oil can mean several things: opaque colour hints toward oil contaminated with other moisture (water or unwanted chemicals). The original oil colour having become a shade darker hints towards aged oil, which may have become too thick or syrupy (too viscous). Oil colour mixed with a black hue hints toward soiled or spent oil. In all cases: change it for the right amount of fresh oil. Ask for a good grade of air compressor oil. Mentioning "air compressor" specifically at a knowledgeable quality tool store will produce the right sort. Many manufacturers have a special air compressor product range, like the "Tellus" line from Shell. If not available, you can use a good quality standard 10W30, which is a thinner "winter type" motor oil but still has the right viscosity and lubricating properties for even a hot compressor. 20W50 may give your compressor startup troubles in cold months.

greetings

gerhard