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

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John Rudd:

--- Quote from: S. Heslop on May 18, 2015, 04:40:41 PM ---

That's interesting. Would a regular household CO detector work in spotting that?

--- End quote ---
Hmm....depends on the sensitivity of the detector or the amount of CO present.....

S. Heslop:
Finally got around to this. Just pressure tested the reciever to 20 bar and held it there for i'd say about 15 minutes without any problems or noticeable drop in pressure. I'm glad one of the fittings matched the pressure test pump, and there's just a plate clamped down over a flange to seal that.

I tried to get those inspection ports off using a giant stillson but even with the thing tied down to the bench neither of them would budge.

I've also taken the regulator apart. Seems like a good amount of water got inside and it was full of rust, all from that one rod in the middle (it's cleaned up in this photo). The seals all look good to me but the brass screw that regulates the pressure was completely worn for half of it, and the other half had some sort of hard varnish dried all around it. No idea where that came from since I doubt any would get inside from a spill.


I've had some problems with the lathe switching itself off lately and I'm fairly sure it's the latching switch at fault, so I had a look inside and managed to lose a part in the process, although the contacts do look pretty terrible so i'm still convinced it's the cause of the fault. I've got a spare one on order. But till then I can't make a replacement screw.

I'm also going to buy a new pressure gauge since one of them is missing its bezel, and probably also a new pressure relief valve since water got into the current one. But so far so good!

JHovel:
Well done S.Heslop.
You've proved that the tank is good to yourself.
For anyone who got nervous about their own tank as a result of the dire warnings here, have  look on eBay for 'ultrasonic thickness testers'. They are getting very affordable. I use one of the cheap ones in my job to check LPG tanks for conformance with standards after they start corroding externally. LPG tanks never corrode inside, but they sit in the weather with nobody caring for them. So they are checked externally every two years here and internally every 10. That is when the safety valve has to be replaced (often with an old one that has been retested and reset)  - and gives an opportunity to shine a torch inside to confirm the lack of internl corrosion.
These tanks are only retested to test pressure if they are repaired in some way (forklift dent, severe corrosion, house fallen onto it etc).
When we find external corrosion, we scrape all the rust off, wire brush the area, pick out all the muck out of the deepest spot we can find and then use the ultrasonic thickness gauge to see what's left. That gets compared to a good part and we have tables to look up the remaining stength/safety for a given wall thickness in a given tank dimension built to a given design standard. If it's below that the tank gets condemned and either then repaired or scrapped by the gas company.
That's just interesting context information.
These cheap ultrasonic gauges are surprisingly good and read to 0.1mm or better metal thickness. I find mine very handy in the workshop for quickly checking sheetmetal thicknesses, pipe wall thicknesses and steel of any kind where it is impossible or inconvenient to measure the edge with a vernier caliper. My cheapy goes to 200mm thickness. Calibration is done with a test piece 4mm thick and you can always easily confirm it's meaurement against something you can measure with a vernier gauge to confirm.
Might be opf interest to others here.
Cheers,
Joe

JD:
Simon, during my career in the RN as an engineer I used to teach maintenance of diving equipment, when our bottles were due for test we sent them out under civilian contract, the bottles were cleaned (inside and out) inspected then tested to one and a half times their working pressure then stamped around the neck of the bottle, you should find your compressor tank should have been tested to the same standard.
There should be metal stamped on the tank date of test working pressure and test pressure. This system even covers marine boilers,traction engines and the capachino machine in your local cafe.
Testing with water, if the tank decides to let go you get wet feet if testing with compressed air serious injury will happen.
I'm not saying you should not test your tank but make sure you have no air what so ever in the tank or from pump to tank ( as we all know I hope you can not compress a liquid but put pressure on it)
JD   

S. Heslop:
Alright! I got it all back together and it works. The regulator is regulating. I forgot if I mentioned it but the old thread in the regulator had completely worn away and needed replacing. The original had a sawtooth thread form but I just replaced it with a regular M8. It might not last for as long as the original but it's not too much of a hassle to replace.

There's one noticeable leak at the valve at the back. There's two valves, one for releasing trapped water and a larger one I assume for letting the air out or maybe connecting it to another tank. I could just replace that with a blanking plug at some point.

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