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

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RobWilson:

--- Quote from: appletree on May 17, 2015, 02:22:18 PM ---
--- Quote from: hermetic on May 17, 2015, 10:59:21 AM ---Right! I am going to stick my oar in here, as I have had this argument on a few sites, and seen all the horror stories and pictures. If you look at the pics and THINK about it, you will notice that the tanks which have exploded or split wide open, are all modern tanks, and show no signs of rust damage whatsoever! the failures have been caused by over pressure where the pressure switch and/or safety valve have failed. Rust causes pinholing, which immediately releases the pressure. You will also see in the pics how frighteningly thin the modern tanks are. I have a British made Broomwade Tank with a 22 cu ft min compressor on it. The tank was made in 1944 and tested to 300psi giving it a safe working pressure of 150psi. The steel used to make the tank is about 3/8" thick. When I was in business in the 1970s this compressor was annually inspected by my insurer and the form showed
" internal rust pitting to a depth of 1/16" When I asked the engineer who did the testing if this was cause for concern he laughed, saying that if it had taken 30 years to corrode that far, there was still a lot of life in it! He also told me that "catastrophic failures are caused by overpressure, not rust" He always spent far more time checking the pressre switch and relief valve than he did on the inspection inside the tank.
 Testing the tank is fairly simple, you need one of these
http://www.ebay.co.uk/itm/PRESSURE-TEST-PUMP-REMS-PUSH-EQUIVALENT-/231560548944, and a hosepipe, stand the tank on end, dome upwards, so it fills completely with water, attach the pump and pump up to twice the working pressure, and leave for one hour. Water is incompressible, so there is no danger involved in this test, as there is no stored energy (actually to be pedantic, there is no expansive energy beyond 300lbs ,assuming a working pressure of 150lbs), the tank cannot explode, it will merely start to leak if there is any weak areas. If it holds for an hour with no appreciable water loss it is safe. This is how most pressure vessels are tested. Actually using twice the working pressure is a more stringent test than is used nowadays, but it errs well on the safe side. If the test certificates issued with chinese compressor tanks are as accurate as the test certificates issued with their machine tools, the failure rate of imported compressor tanks is unsurprising.
Phil

--- End quote ---
Hi not being an a**e did you mean to post the pictures or have I missed something?

--- End quote ---


Yup your missing something  :D ,,,,,,,,,,,,,,,,, Phil was referring to photos of tank failures that maybe found on the WWW ,


Rob   

petertheterrible:
Something that has really bugged me over the years is that the laws regulating an item are not universally applied. 

Looking at most of these 'economic imports' you'll probably realize that they would never have passed the inspector if they would have been produced locally.  What a way to kill economic growth, overburden the local guy with strict and in my view necessary safety regulations while the other guy's pass under the radar.  (Just please don't give the inspector wind of me.)

Something I have seen a couple of times in recent years is Italian made shop tools with sqeeuberish on some of the parts.  So be aware of what you are buying.

As for the problem at hand I still say a long extension cord is a must for the first start up of a 'look fine but hope not to pee my pants when it goes compressor'.  As for everyday use, a 10 meter pipe would be nice. 

steampunkpete:
You have a compressor that is 1/3 century old. You don't know its maintenance history except that it has been lying around unloved for some years. There is some evidence that it hasn't been maintained.

Unless you do some testing such as suggested by Hermetic, you will only be guessing at its integrity.

You are worried about your safety. How much is your safety worth to you? Is it worth £120? Because £120 is the price of a new entry-level compressor at your local Homebase.

Is using this worth the risk to you? - after all it seems that you have it because it is free, not that you have any real need.

As an aside, pressure cylinders do not "explode". They are designed to fail by tearing so as to avoid the generation of fragments. If such did happen for a receiver of this type and size, I suspect the result would be loud; the compressor might well fall over and a lot of dust would be made air-born. A frightening experience.

None the less, get the thing down the dump and go to Homebase on your way home.

dawesy:
Why throw away what may be a perfectly serviceable compressor?
Personally I'd change the relief valve for a new unit plug it in at the bottom of the garden and try it ( obviously stand away from it) as already stated if the tank has rusted then a pinhole will have formed and it will simply leak not explode.

RussellT:
There are many people for whom £120 is a significant sum of money.

I'd certainly test it before dumping it.  I'd check the safety valve isn't stuck then I'd plug it in and let it pressurise a bit, and check that the safety valve releases the pressure.  I might check the gauge with a tyre pressure gauge.  Then, from a safe distance I'd let it run and see if the regulator worked.

If you decide to dump it you'd probably get £20 putting it on ebay for spares or repair.

Russell

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