Author Topic: Compressor safety, or how do I make sure an old compressor is safe?  (Read 21921 times)

Offline steampunkpete

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #50 on: May 18, 2015, 06:11:54 AM »
I take your point about 120 being a lot of money to some, but that doesn't change the comparison between and potential injury. If one can't afford to do something with a reasonable degree of safety, then the choice must be either not to do whatever it is, or to somehow make it adequately safe or take a gamble.

I too would probably keep it by spending some dosh on some new gauges, hoses and regulator, which is certainly less than the cost of a new compressor. However, I would strip the whole thing down and assess whether I was spending out for those parts to prop up a compressor already beyond its working life or knackered through neglect.

A risk is there but, in perspective, it isn't enormous.  Check the safety valve function and visually inspect the interior. If the interior looks pristine then replace the hoses, gauges and regulator. If the interior looks significantly degraded then do the hydraulic test, (being careful to full expel all the air) although if it were me, I'd throw it away at that point (drill holes in  the receiver and take it to the dump).

Luna AB is a Swedish company, its name and address are on the plate in the plate in the photo. (http://www.luna.se/)
All materials are compressible, including water, but water has such a high modulus that it can be regarded as incompressible for almost all purpose (and, counter-intuitively, it has the property that in a completely degassed state it will sustain a significant tensile load)

Offline petertheterrible

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #51 on: May 18, 2015, 07:52:14 AM »
I have been nearby when a large compressor used on a mine site 'exploded'.  I am not the jumpy type, the noise was not comparable even with that of a big bore rifle.  But the effect on everyone was astonishing, utter quietness befell everyone, but the strangest thing was that the atmosphere felt different afterwards.  Not a bomb, not a hand grenade throwing shrapnel everywhere, but damn it got hot there pretty quickly. 

One cannot put a price on ones own life or that of the people working for you.  Two lessons I have learned from two salty dogs the one a marshal at the range who asked me where my safety was, when I replied that it was a single shot without a safety he said that the only safety I had was the 11 kg mass between my ears.  The other was the local engine builder doing business for over 40 years, when I asked him if it wasn't dangerous when they dino'ed engines, he pointed to a hole between my feet and said that if was safe within reason everywhere but there.
Terrible by name, worse by profession.

lordedmond

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #52 on: May 18, 2015, 09:19:42 AM »
OT

But one sign brings it home re safety at a joiners shop they had a 48 inch circular saw one of the large machine which I did maintain on it read


" please count your fingers after use "

The other machines included a good number of 300 HP compressors a couple of which were synconos motors to enable us to bring up the PF by altering the exitaition

To the OP please think about that old compressor of unknown history simply put as others have said is " is it worth it " at least it's air not steam but that's a totally different animal in pressure vessels

Be safe
Stuart

Offline hermetic

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #53 on: May 18, 2015, 01:31:16 PM »
What would I do with it? I would test the pressure guage against a known good one, then check the pressure relief valve and the pressure switch for operation, then use it! I will say it again, Catastrophic failure is caused by overpressure, not corrosion, therfore inspecting the inside of the tank will tell you very little. If it has rust pitting it may pinhole and leak at some time in the future, if it starts up, and does not cut out, and the relief valve is stuck, be prepared for a very big bang. The pressure switch and overpressure relief valve are much more important, as is regular draining. I would not use any silicon based anti rust product inside a compressor tank if you are ever going to spray paint with it.
phil

Offline hermetic

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #54 on: May 18, 2015, 01:32:49 PM »
PS, sorry for the confusion over the pictures!

Offline vtsteam

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #55 on: May 18, 2015, 01:42:17 PM »
My guess is it's likely to be fine. I'd check out the water filled tank with my homemade test pump and gauge as mentioned early on in this thread.

If that was good, I'd empty and reconnect. The only other thing to worry about is the pressure switch/pressure relief valve not working. I'd check that over visually, note the cutoff/relief pressures.

Then I'd plug the damn thing in on an extension cord outside. Since the compressor has a gauge I'd wait for it to hit cutout pressure, and if it went 5 lbs above that I'd pull the plug. Likely it will work fine.

If it doesn't cut-off when it is supposed to I'd buy a new valve and feel I'd checked more than the average homeowner/construction crewman with a couple year old compressor and feel I had a safer machine than they do as a result. A separate pressure safety valve can be pulled out to see if it's free and also checked the same way with the pressure gauge.

The argument re. how much is your life worth compared to the supposedly low cost of something can be applied to anything that has dangers, including buying a box of matches, a candle, or a bag of marbles. Don't do it if the envisioned dangers outweigh the desire for a romantic dinner or a game played in the dirt.  :)
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Offline Fergus OMore

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #56 on: May 18, 2015, 02:23:21 PM »
I'd do the same as Steve( VTSteam) and run a water test but defintely not air.

This, if you think about it is exactly how Aqualung tanks ( which have to stand 3200psi ) are tested.

If they burst- well, no matter. They are not going to go into orbit.

However, compressors new are LESS than 90 from places like Aldi. They come with a 3 year guarantee.

Point made?
If it it isn't, I went for a bigger MIG bottle today--say no more.

Norman

Offline Pete W.

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #57 on: May 18, 2015, 02:42:13 PM »
Hi there, Simon and all,

All I have to contribute to the discussion on testing is that IMHO there is no merit in over-testing, it just risks needless damage.  I'd advise careful research to make the best possible attempts to discover the manufacturers' specified working and test pressures and keep below them.

I do have another point, however.  When I was involved with a team maintaining club SCUBA equipment many years ago, we were made aware that oil lubricated air compressors can experience pseudo-Diesel explosions in the cylinder at TDC.  These don't harm the compressor but they're very bad for the air quality.  The combustion is incomplete and produces Carbon Monoxide, a serious No-No for breathing air.  I don't know whether the compression ratio of your compressor is high enough to cause this phenomenon but ...

I was reminded of this by the photo of the ventilated face-mask in your post on the Car Boot Sale thread - if you intend to use this compressor to feed a face-mask get hold of a Carbon Monoxide detector and check the air quality, often!  We don't want to lose you!   
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Pete W.

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Offline chipenter

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #58 on: May 18, 2015, 03:12:39 PM »
I am using a scuba tank as a resovour , it has stamped on the neck tested to 300 bar , my compressor cuts out at 6 bar quite a margin .
Jeff

Offline S. Heslop

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #59 on: May 18, 2015, 04:40:41 PM »
Hi there, Simon and all,

All I have to contribute to the discussion on testing is that IMHO there is no merit in over-testing, it just risks needless damage.  I'd advise careful research to make the best possible attempts to discover the manufacturers' specified working and test pressures and keep below them.

I do have another point, however.  When I was involved with a team maintaining club SCUBA equipment many years ago, we were made aware that oil lubricated air compressors can experience pseudo-Diesel explosions in the cylinder at TDC.  These don't harm the compressor but they're very bad for the air quality.  The combustion is incomplete and produces Carbon Monoxide, a serious No-No for breathing air.  I don't know whether the compression ratio of your compressor is high enough to cause this phenomenon but ...

I was reminded of this by the photo of the ventilated face-mask in your post on the Car Boot Sale thread - if you intend to use this compressor to feed a face-mask get hold of a Carbon Monoxide detector and check the air quality, often!  We don't want to lose you!

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

Offline John Rudd

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #60 on: May 18, 2015, 05:00:33 PM »


That's interesting. Would a regular household CO detector work in spotting that?
Hmm....depends on the sensitivity of the detector or the amount of CO present.....
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Offline S. Heslop

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #61 on: July 13, 2016, 05:44:42 PM »
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!

Offline JHovel

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #62 on: July 14, 2016, 10:48:12 AM »
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
Cheers,
Joe

Offline JD

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #63 on: July 14, 2016, 12:48:28 PM »
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   
If you cant fix it hit it with a bigger hammer

Offline S. Heslop

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #64 on: July 21, 2016, 10:04:45 AM »
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.