Author Topic: Compressor safety, or how do I make sure an old compressor is safe?  (Read 22075 times)

Offline wgw

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #25 on: May 15, 2015, 09:33:31 AM »
A small tank like that (well it looks small from here) would be no worse than a car tyre bursting really. My cheap compressor is about 20 yrs old and I've had no problems. Bought new pressure switch and safety valve and drain regulary. A good tap all round the tank will show any badly corroded areas.

Offline mattinker

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #26 on: May 15, 2015, 09:40:20 AM »
A small tank like that (well it looks small from here) would be no worse than a car tyre bursting really. My cheap compressor is about 20 yrs old and I've had no problems. Bought new pressure switch and safety valve and drain regulary. A good tap all round the tank will show any badly corroded areas.

I don't agree, the tank is made out of steel and the working pressure well above that of a car tyre. I'm not sure why you refer to your compressor, the state it's in and whether or not it's any good has nothing to do with Simon's compressor!

Regards, Matthew

lordedmond

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #27 on: May 15, 2015, 10:25:00 AM »
It a mine field

First you need to get one or two of the access bungs out then with a boroscope have a good look to see if there are any blisters of rust , then tap on the out side at that site with a ball pane hammer to see if it gives .

If the tank as a name plate it should give you the test details and retest date

Then if all looks ok do a hydro test

Then you need to prove the safety valve and the unloading valve are operating correctly

The electrics should be ok as you have run it

IMHO I would dump the tank as a unknown and buy a new tank and use that instead.

No I am not a pressure vessel inspector but I have seen and had to witness a large number of tests some small some big where the inspector climbed in though the inspection hole.

Stuart

RobWilson

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #28 on: May 15, 2015, 10:29:14 AM »
A small tank like that (well it looks small from here) would be no worse than a car tyre bursting really.

You reckon !   :loco:

Rob

Offline Manxmodder

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #29 on: May 15, 2015, 10:32:22 AM »
WGW,Don't underestimate the damage an exploding car tyre in close proximity to a person would have.  There are plenty of health and safety records of fatal accidents involving exploding tyres,and as Matt says a metal receiver exploding in a confined space would have devastating consequences.......OZ.
Helixes aren't always downward spirals,sometimes they're screwed up

Offline Manxmodder

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #30 on: May 15, 2015, 10:37:42 AM »
A small tank like that (well it looks small from here) would be no worse than a car tyre bursting really.

You reckon !   :loco:

Rob

Agree Rob, that is possibly the most misguided comment I have ever seen posted on these forums  :loco: ....OZ.
Helixes aren't always downward spirals,sometimes they're screwed up

RobWilson

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #31 on: May 15, 2015, 10:41:05 AM »
A small tank like that (well it looks small from here) would be no worse than a car tyre bursting really.

You reckon !   :loco:

Rob

Agree Rob, that is possibly the most misguided comment I have ever seen posted on these forums  :loco: ....OZ.


It sure is  a candidate for a   Darwin award   :lol: :lol:   



Rob

Offline PekkaNF

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #32 on: May 15, 2015, 10:49:36 AM »
I had one incident....the pressure swich did not acivate on one compressor, I was thinkking "It is taking a long time to fill that tank" it show 10 bars on meter (adjusted to 6 bars)....switched it off and bleed, opened the swich and it looked fine. Tried it again and it did work, but I could not trust it, it was one of those cheap replacements "Biltema" which has bad reputation here. I did repace it.

I once build my own compressor...Used proper pressure switch 8 bars, over pressure valve 10 bars, and 12 or 16 bar pneumatic plastic hose between compressor and tank....figured that least I will not blow than tank up with a compressor. It was small tank and tested on 20 or 30 bars, enough safety margin. Anway, I used it long time and it flinaly corroded next to water cock, it did not blow up, just developped a little hole, but I ditched the tank.

Most of the compressors here are build in italy and even though they a build for price, there seem to be very little problems with them. Until someone fixes them with wrong parts.

Just one more items, on one of the first pictures one elbow looks like a cast iron heating pipe fitting...maybe it is just my imagination?

Pekka

Offline Kjelle

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #33 on: May 15, 2015, 01:42:15 PM »
Ok, I'll admit it, I was wrong... That compressor was made in July 1982! Is 33 years old!If it works, I'd be tempted to use the compressor, and ditch the tank for something newer, and possibly bigger...

Kjelle

Offline Manxmodder

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #34 on: May 15, 2015, 03:14:13 PM »
Pekka,that is a good idea to use a piece of pipe with a known burst pressure as a safety fuse.

.....OZ.
Helixes aren't always downward spirals,sometimes they're screwed up

Offline vtsteam

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #35 on: May 15, 2015, 04:23:02 PM »
I know of a guy who lost his hand inflating a wheelbarrow tire. He didn't set the regulator low enough, and it inflated so fast (being small) that it burst while he was holding it down on the bench.

A small vessel can actually be more dangerous than a large one. And a rubber tire is not necessarily "safe".
I love it when a Plan B comes together!
Steve
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Offline wgw

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #36 on: May 16, 2015, 05:37:27 AM »
OK I admit it was a bit of a stupid remark, re car tyre. It was meant to be tongue in cheek. Only excuse is I'd just put a hedge cutter into my leg and was in a bad mood. I've been hurt by tyre blowout, inflating a trailer tyre, that hurt but no damage to me. I knew a man killed by tractor tyre exploding, in the shop these have to be inflated in a cage for safety, but hard to do in the field.

Offline RussellT

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #37 on: May 16, 2015, 01:46:43 PM »
I've often wondered whether the reason you don't hear of more accidents with small compressors is that the failure mode is pinholing as Pekka suggests.

LPG tanks are acceptable as air tanks (apparently even to HSE).  I used a fire extinguisher - I was trying to find a couple of CO2 fire extinguishers as they're normally aluminium but couldn't find any at the time.  Water fire extinguishers have an anti corrosion coating on the inside.

Russell

Offline dawesy

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #38 on: May 16, 2015, 02:55:37 PM »
Yep I too have had this. Mine rusted a 5mm hole in it. I only noticed when I switched it on and heard a hissing noise. As with most things compressed as soon as a failure creates a relief the pressure drops.
The only thing I can imagine causing a tank to explode is weld fracture which would hopefully be found at the manufacture testing point.
Lee.
wishing my workshop was larger :(

Offline petertheterrible

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #39 on: May 17, 2015, 07:43:06 AM »
I believe that although there are many valid points made here I believe that what MexicanJon said is as near to the truth and the best possible advice.

Most small compressor reservoirs are not destructively tested these days, factories get away with not a lot of testing, please take that in consideration.

If someone considers himself still inexperienced in compressors and pressure vessel workings I would not advice him in repairing safety valves but to throw away and buy new.  Regulators and other valves although not to difficult to comprehend the workings of do present some difficulty for a novice.  For one how do you test a valve setting safely without proprietary equipment of a working compressor and good regulator.

Something to take in consideration is that in the testing of pressure vessels like these the 'swelling' of the vessel is also taken into account and all data is compared to a perceived determined standard.

The other guy may be misconstrued about the power a bursting tire has, but it is still regular practice in some boilermaking circles to ping test a boiler by striking it and listening to the sound it makes.  Burst discs and safety devices of regulated burst qualities are available but I reckon that that that is widely known to all informed members.

Although I have yet to see it in practice testing vessels, the non invasive electronic type testers used to test welds might be of use for the hobbyist to test pressure vessels.  The neon ink I believe may not be a true indicator as it requires an existing crack or external bad spot.

I believe that the best safety device if the filling pipe.  The greater the distance between yourself and the compressor, the better the chance that you won't get hurt.  I have seen the aftermath a brand new industrial compressor left due to their being fiddled with it/ not installed properly.  Just because it's new doesn't necessarily mean it's safe.  I would after visual inspection when draining water (look for rust) probably take the unit out back as far as possible from anything that can be damaged and run it, while just peeping to see if it shuts of around a sturdy wall. (Just my personal method and I don't advice anyone to follow.)
Terrible by name, worse by profession.

Offline hermetic

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #40 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

Offline petertheterrible

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #41 on: May 17, 2015, 12:32:47 PM »
Your a braver man than me bringing the Chinese into the story, but it this case it actually does hold water.

Metal used on old tanks was normal boiler plate.  These modern tanks are made of thinner metal that is stronger but in my opinion corrode more easily when they are not treated with some sort of silicone preservative film at the factory.

What would your best advice be in using the compressor in the picture, hermetic? Use/not use/ test?
Terrible by name, worse by profession.

Offline appletree

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #42 on: May 17, 2015, 02:19:44 PM »
A wonder how many people have bought, "cheap" compressors from the east and kept using them without a second thought as they bought them "new" and know the history . My parents used to have a compressor in their Hire fleet about 12 cfm which used the heavy duty 2 inch OD tube frame as the pressure vessel. It did not have any test plate etc it was my understanding that as it was made from a given class of steel tube/volume it was not considered a pressure vessel. This could be understandable as the distribution air pipework in industry is not tested or inspected.
 

Offline appletree

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #43 on: May 17, 2015, 02:22:18 PM »
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
Hi not being an a**e did you mean to post the pictures or have I missed something?

Offline Lew_Merrick_PE

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #44 on: May 17, 2015, 02:47:01 PM »
Topic Drift Alert  Whereas I am sure that there are good shops & suppliers in China, I have yet to run into one.  A few years ago while doing work for a company that likes to claim that they are the largest American employer of Chinese workers we need material certificates to be supplied with parts.  The supplier in question asked for a sample of such a material certificate.  I sent them one for an entirely different material (rhenium bar for a rocket nozzle) and they sent it back to us with only the material identity changed out.

My customer on this project accepted it as genuine!  That was the last time I did work for this particular company.  They are a major, world-wide purveyor of consumer and industrial products...

RobWilson

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #45 on: May 17, 2015, 03:11:28 PM »
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
Hi not being an a**e did you mean to post the pictures or have I missed something?


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


Rob   

Offline petertheterrible

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #46 on: May 17, 2015, 03:30:05 PM »
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. 
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Offline steampunkpete

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #47 on: May 18, 2015, 02:06:29 AM »
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.

Offline dawesy

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #48 on: May 18, 2015, 02:52:41 AM »
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.
Lee.
wishing my workshop was larger :(

Offline RussellT

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Re: Compressor safety, or how do I make sure an old compressor is safe?
« Reply #49 on: May 18, 2015, 04:46:10 AM »
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