Author Topic: Compressor safety, or how do I make sure an old compressor is safe? (Read 29959 times)

S. Heslop · « **on:** May 14, 2015, 11:53:32 AM »

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 · « **Reply #1 on:** May 14, 2015, 12:13:00 PM »

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....

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 · « **Reply #2 on:** May 14, 2015, 12:17:47 PM »

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 · « **Reply #3 on:** May 14, 2015, 01:19:36 PM »

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 · « **Reply #4 on:** May 14, 2015, 01:37:49 PM »

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.

Kjelle · « **Reply #5 on:** May 14, 2015, 01:57:25 PM »

That is a quite good compressor, sold by LUNA, a Swedish company... I doubt it's as old as your neighbour says, I'd say maybe 20 years.... LUNA is still in business, do a google, and you'll find them. I think they might stock whatever parts you need, and there might even be a spare parts list and sketch on their website...

It was touted as better than the Chicom stuff other were selling at the time it was new, I think they were made (partly) in Italy... Don't quote me on that!

Kjelle

S. Heslop · « **Reply #6 on:** May 14, 2015, 03:07:50 PM »

Quote from: vtsteam on May 14, 2015, 01:37:49 PM

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.

Found the thread where you made that pump.

http://madmodder.net/index.php/topic,9920.50.html

So I figure the way to do things would be to take the thing apart and plug all the holes, test it to about 200 or more psi, then reassemble it and keep an eye on the gauges as it fills to make sure the motor cuts off at the right points. Is it at all likely that the gauges will be out of calibration? I suppose I could test the relief valve too while hydrotesting it.

Also there's a few plates on the tank that say that it was made in 1982. In Swedish and Italian. It's Italian made it seems.

It seems my favourite image host has gone down. Hopefully not for good, but good image hosts never seem to last for too long. I guess they're only losing money unless they're pulling some bullshit like photobucket or imgur.

awemawson · « **Reply #7 on:** May 14, 2015, 03:40:26 PM »

[quote author=S. Heslop

It seems my favourite image host has gone down. Hopefully not for good, but good image hosts never seem to last for too long. I guess they're only losing money unless they're pulling some bullshit like photobucket or imgur.
[/quote]

That's why I always upload pictures to the forum rather than use a third party. That way the images are always there so long as the forum survives. Nothing worse than reading an interesting old thread where the pictures have all gone

appletree · « **Reply #8 on:** May 14, 2015, 03:52:14 PM »

Most receivers only have small inspection openings, so even the official insurance inspector can only assess using his eyes and aids such as mirrors etc. At work we had air receivers little larger than yours the Inspector only had a 2 inch diameter hole to look through admitted they were heavily constructed but they never went away for pressure testing. Have you considered contacting the manufacturer for advice, or a pressure vessel tester for their opinion on the way forward for a receiver of this class.

appletree · « **Reply #9 on:** May 14, 2015, 03:59:08 PM »

Just had another look at your pictures, I think the vessel is better quality than suspected, the wall thickness of the inspection plug boss is of a good section and I would say the hole large enough to inspect through, after all that is what it is there for rather than a small pipe connection.
Any rust is likely to be at the lowest point a dentists type mirror would allow you to see, even if condensate has rested in the bottom it still needs oxygen for rusting to occur.

S. Heslop · « **Reply #10 on:** May 14, 2015, 04:30:27 PM »

Quote from: awemawson on May 14, 2015, 03:40:26 PM

That's why I always upload pictures to the forum rather than use a third party. That way the images are always there so long as the forum survives. Nothing worse than reading an interesting old thread where the pictures have all gone

I wish i'd done that sooner. I trusted iforce.nz since its been up and stable for a good few years now. I figured you wouldn't be able to embed attached pictures but it seems to be working fine. If iforce doesn't come back i'll probably go through my old threads and attach the pictures, i've kept them sort-of organized in folders.

S. Heslop · « **Reply #11 on:** May 14, 2015, 04:34:23 PM »

Quote from: appletree on May 14, 2015, 03:59:08 PM

Just had another look at your pictures, I think the vessel is better quality than suspected, the wall thickness of the inspection plug boss is of a good section and I would say the hole large enough to inspect through, after all that is what it is there for rather than a small pipe connection.
Any rust is likely to be at the lowest point a dentists type mirror would allow you to see, even if condensate has rested in the bottom it still needs oxygen for rusting to occur.

I imagine in a compressor there's plenty of oxygen about. Corrosion might be a concern but i'm also worried about fatigue. Hydraulically testing it would put me more at ease than just checking for corrosion.

appletree · « **Reply #12 on:** May 14, 2015, 04:59:25 PM »

Obviously when in use there is plenty of oxygen about in use but if the vessel is unused and the valves shut the oxygen will become depleted. I would inspect either way, going back to my earlier post as to what happens in industry, i do not see why the vessel would be fatigued, the vessel is designed in the first place even if the safety valve is not working which you can check, the maximum pressure achievable is determined by the compression ratio of the compressor.

vtsteam · « **Reply #13 on:** May 14, 2015, 05:14:38 PM »

There's been plenty of oxygen and moisture condensation in most any compressor tank that's been used. That's why they put drains on the bottom. And likely rust, at least surface rust.

If your eyes can determine rust thickness under scale over every square millimeter of the inside of a tank through a borescope, and you know the thickness and composition of the metal and can then calculate the allowable stress left after deductions for the rust locations you've found, then that's the way to go.

Otherwise a pump you can make yourself and a reasonably priced gauge will actually tell you the strength of what you have to the degree you are interested in.

David Jupp · « **Reply #14 on:** May 14, 2015, 05:25:50 PM »

In an industrial setting PSSR would apply - which requires a scheme of examination to be in place. Such schemes would be pretty similar for most compressors around this size - manufacturers often supply one with the machine (so may be worth asking).

Test pressure should be marked somewhere. For smaller vessels, the original plan could have been no routine test, but with a 'use by' date - though the label shown looks like it has space to record routine tests.

vtsteam · « **Reply #15 on:** May 14, 2015, 05:30:46 PM »

One other suggestion if you are worried or if on examination or test you don't like what you see..... buy one of those refillable portable air tanks and replace your present one. They're pretty reasonably priced.

Lew_Merrick_PE · « **Reply #16 on:** May 14, 2015, 06:12:17 PM »

Your local welding gas company should be able to provide you with a pressure test & certificate for a reasonably low cost. ???

Henning · « **Reply #17 on:** May 15, 2015, 04:15:45 AM »

Does it say anything more than Luna compact on the side of the tank? There should also be a sign somewhere...
If it does, i may be able to help with schematics and/or parts lists and maybe even a user manual.

mexican jon · « **Reply #18 on:** May 15, 2015, 05:07:11 AM »

I really do have to commend everybody on being so safety conscientious

but re-hydro testing a small compressor that probably has had little usage is probably going to cost more than what a new one could be purchased for

. The big difference between a compressor and a boiler (I know they are both pressure vessels) is compressors have a set pressure control and a pressure relief valve and they charge to the set pressure at a given rate. Boilers whilst having a pressure relief valve basically get to pressure as quickly as you can heat the water and therefore are more susceptible to stress damage

.

I’m not for 1 minute saying that compressors don’t go bang because they do but generally a compressor that has been used in a stable inside environment will very rarely have a tank that won’t outlast the pump or other components

.

But as I said at the start I really do have to commend everybody on being so safety conscientious

My main compressor in the workshop was built in 1948 and is still going strong

.

mattinker · « **Reply #19 on:** May 15, 2015, 05:21:33 AM »

Simon,

Plug all the holes, fill the tank up with water and inflate with a high pressure bicycle pump! I use the metal valve holder from an inner tube silver soldered into a screw plug to connect the pump. Commercial vehicle tyre fitters will give you old inner tubes. Pump up to twice the working pressure to test. I have a 500 litre tank that I need to test, half a ton of water to fill it up! An other alternative high pressure pump is a pressure washer.

Regards, Matthew.

mexican jon · « **Reply #20 on:** May 15, 2015, 05:56:39 AM »

We normally test 1.5 times max working pressure for the initial test and certification

then periodic testing would be to max working pressure

. And just so you know our normal working pressure is 15000 PSI (yep fifteen thousand)

This is for receivers rather than boilers (don’t know if boilers are 2 times max design working pressure)

edward · « **Reply #21 on:** May 15, 2015, 06:56:20 AM »

if you have a Scuba shop near you they will have the tools to look inside, and an ultrasound thickness measuring device if there are any dodgy spots. it might cost, dependant on how nice they are feeling.

edward · « **Reply #22 on:** May 15, 2015, 07:00:42 AM »

Forgot to add: not all Scuba shops test in house, so it would need to be one that does.

Scuba cylinders are typically 232bar WP and 348bar TP made of steel and used in salt water, so divers tend to be quite anal about testing.

David Jupp · « **Reply #23 on:** May 15, 2015, 07:18:04 AM »

Stick to the test pressure on the label - (I don't read Swedish, but it looks like 8 bar test with 7 bar working ?). Certainly don't try 2x working - you may cause damage.

awemawson · « **Reply #24 on:** May 15, 2015, 07:23:57 AM »

Simon,

I have a pressure test pump like the one in the picture below and would willingly test your tank were distances and geography not such a challenge. Though I must confess I've never hydro statically tested my compressor tank just regularly drained condensation and given it a visual check over (it's in an otherwise unoccupied steel Portakabin - if the worst happened it would be contained)

wgw · « **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.

mattinker · « **Reply #26 on:** May 15, 2015, 09:40:20 AM »

Quote from: wgw 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.

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 · « **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 · « **Reply #28 on:** May 15, 2015, 10:29:14 AM »

Quote from: wgw 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.

You reckon !

Rob

Manxmodder · « **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.

Manxmodder · « **Reply #30 on:** May 15, 2015, 10:37:42 AM »

Quote from: RobWilson on May 15, 2015, 10:29:14 AM

Quote from: wgw 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.

You reckon !

Rob

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

RobWilson · « **Reply #31 on:** May 15, 2015, 10:41:05 AM »

Quote from: Manxmodder on May 15, 2015, 10:37:42 AM

Quote from: RobWilson on May 15, 2015, 10:29:14 AM
Quote from: wgw 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.

You reckon !

Rob

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

It sure is a candidate for a Darwin award

Rob

PekkaNF · « **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

Kjelle · « **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

Manxmodder · « **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.

vtsteam · « **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".

wgw · « **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.

RussellT · « **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

dawesy · « **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.

petertheterrible · « **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.)

hermetic · « **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

petertheterrible · « **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?

appletree · « **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.

appletree · « **Reply #43 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

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

Lew_Merrick_PE · « **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 · « **Reply #45 on:** May 17, 2015, 03:11:28 PM »

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

Yup your missing something

,,,,,,,,,,,,,,,,, Phil was referring to photos of tank failures that maybe found on the WWW ,

Rob

petertheterrible · « **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.

steampunkpete · « **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.

dawesy · « **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.

RussellT · « **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

steampunkpete · « **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)

petertheterrible · « **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.

lordedmond · « **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

hermetic · « **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

hermetic · « **Reply #54 on:** May 18, 2015, 01:32:49 PM »

PS, sorry for the confusion over the pictures!

vtsteam · « **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.

Fergus OMore · « **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

Pete W. · « **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!

chipenter · « **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 .

S. Heslop · « **Reply #59 on:** May 18, 2015, 04:40:41 PM »

Quote from: Pete W. 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!

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

John Rudd · « **Reply #60 on:** May 18, 2015, 05:00:33 PM »

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?

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

S. Heslop · « **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!

JHovel · « **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

JD · « **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

S. Heslop · « **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.

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Author Topic: Compressor safety, or how do I make sure an old compressor is safe? (Read 29959 times)

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