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Compressor safety, or how do I make sure an old compressor is safe?

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S. Heslop:
A neighbor across the road who restores old cars gave me a spare compressor he had in his shed. I'm pretty excited about it!



But being fairly old (about 30 years), and having sat in a shed for a while, i'm nervous about it possibly being dangerous. It runs fine and I got it up to 40psi before deciding that was far enough. There's a large plug on the back with a valve for getting the water out that I could possibly remove to inspect the inside of the tank, but I thought i'd probably best not remove it until asking if it was necessary.



The guy also said that the output regulator is shot and leaks air, although it isn't currently it probably will start doing it again if I try fiddle with it. I can't find any information on this compressor online and i'd have no idea how to go about potentially repairing it.

Anyways any advise is appreciated.

John Rudd:
A new regulator is the least of your issues......you can pick one up from eBay or machine mart....

In order if importance.....

A hydraulic test of the receiver if you have doubts about it......
The relief valve, needs testing to make sure it goes at the correct pressure, which should be below the MWP of the receiver, around 120 psi ....
The pressure switch, should stop the pump at its set pressure....the setting needs to be below the relief valve setting....100psi.....would be ball park.....the differential on the switch doesn't want to be too wide or too narrow....if the switch is set to trip at 100, then 75-80 psi should be a decent value for resetting...
None of these figures are cast in stone, mainly dependant on the pump...but ought to be a start for you...obviously if you aren't going to use the compressor for anything serious and just for a bit of spraying, then the settings could be lowered if you have any doubts.... :zap:

I'm sure mine will not be the only opinion expressed......


If you are up sure about anything shout up.....don't take risks....compressed air is just like any other compressed gas and can be just as dangerous, but you already know this.... :)


If you have access to a megger, you could quickly zap the motor for a quick insulation test.....

David Jupp:
Main potential hazards are probably, receiver corroded and weakened, relief valve jammed or restricted, loose pipe or fittings coming adrift under pressure.  Oh, and not forgetting electrical hazards

I'd suggest, inspect receiver via one of the plugs/fittings (the difficult bit is to decide how bad things are if you do find corrosion).  Strip and clean the relief valve to make sure it operates freely and that there are no restrictions (that should protect things even if the pressure switch isn't working.  Make sure everything is securely attached.  Small Jubilee type clips are often frowned on for securing flexible air hoses (but realistically they are still widely used) - use something better if you can find it.

Check condition of plug/cable, make sure earth is connected. 

Replace that clear reinforced hose - it has probably gone very stiff/brittle.

appletree:
The Air receiver is the more difficult bit to check, these type of compressors tend have rather thin receiver walls. Obviously corrosion, particularly pitting is the big issue, if you can borrow a borescope (Lidl do them) you could inspect through any of the connection ports and soon decide the condition. Other options are do away with the receiver altogether, operate at lower pressure, however there is still a lot of force available at 40 psi. There is no need to have the compressor near you as long as you keep pipework large enough to avoid pressure drop. Visual inspection in some form is the order of the day   

vtsteam:
I think inspection on practically any tank through a borescope (and I have one) won't tell much except to show that yes, in most tanks unless right off the showroom floor, there will be some rust. But how much, how bad? You can't really tell that by sight.

If it was mine, I'd fill the tank with water and hydrotest it to about double what I'd want to run it at, and hold it for a minimum of 5 minutes checking the gauge. If it's filled with water, it can't explode, just leak.

If you look elsewhere on this forum you'll find a boiler feed and hydrotesting pump I made from scratch. You just need that and a decent liquid filled pressure gauge in the range you want to check (maybe $10 on ebay).

One of the handiest things I've made here, and definitely something that can provide peace of mind.

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