Air Compressor Warning

[Gary WoodingParticipant @garywooding25363]

I took a careful look at the tank, which still looks new, and found that the date of manufacture was 1992. I've ordered a new compressor.

[Glyn DaviesParticipant @glyndavies49417]

Since I have a 150psi, 50 litre compressor under my bench, this post gave me a bit of a fright. Mine's an Airpower similar to that shown in one of the later videos. At 3mm wall thickness, the hoop stress in the tank at 10 bar is 44MPa, giving a 5x safety factor against the 2% proof stress value for MS. And way below the fatigue limit for MS. Even at 2mm thickness, the SF is still about 3.5.

In the OP's video, he thinks the failure initiated at a seam, not where the worst rust from condensate was, and I saw that the delivery pipe from the pump seemed to have blown off the unloader valve. So I wonder if the failure was due to overpressure.

[larry phelan 1Participant @larryphelan1]

I drain my tank every time I use the compressor, only takes a few minutes, but surprising how much water comes out..

[CirclipParticipant @circlip]

Was stunned to learn that the Chemical firm at the bottom of my garden were carrying out a pressurised process (which failed) resulting in neighbours in close proximity being compensated for their washing hung out to dry and having cars parked close to the "occurrence" being professionally cleaned.

As an Ingineer I was horrified to learn the ONLY safety feature on the process was a burst disc.

Regards Ian.

[Danny M2ZParticipant @dannym2z]

Posted by not done it yet on 24/01/2021 14:08:45:

When you look at some tanks the drain is not actually at the very bottom.

ndiy. I asked the same question a few years ago and never got a satisfactory answer but then the manufacturers must have a resun for this layout, Slill windering why?

[Howard LewisParticipant @howardlewis46836]

Bursting discs are not proof against damage where explosions are concerned.

They used to be a feature of main propulsion marine engines., but the varnished brown paper variety were found not to be safe where crankcase explosions were concerned.

Photographs have been published showing two flights of steel stairs, from cylinder head to bedplate, on the engine severely twisted; but the disc was still intact. The rate of pressure rise is such that the damage is done before the disc can rupture.

Many years ago, Blackstones experimented with "explosion proof" crankcase doors. A colleague told me of a door weighing over 50 Kg being thrown across the shop!

A colleague was beside an engine which suffered a crankcase explosion. The die cast sump fell onto the bedplate, leaving the flange still securely bolted to the crankcase.

I witnessed a crankcase explosion, in a car engine, from across a car park. Quite frightening and damaging!

A colleague lost the ends of fingers when an air receiver exploded, because the oil carried over, vapourised and mixed with the air, exploded.

For air receivers, frequent draining of condensate HAS be a safety measure.

Howard

[SillyOldDufferModerator @sillyoldduffer]

Posted by Danny M2Z on 25/01/2021 11:59:01:

Posted by not done it yet on 24/01/2021 14:08:45:

When you look at some tanks the drain is not actually at the very bottom.

ndiy. I asked the same question a few years ago and never got a satisfactory answer but then the manufacturers must have a resun for this layout, Slill windering why?

Pretty sure it's to stop liquid collecting in the drain cock and corroding it.

I don't tilt my compressor to drain it. Rather I leave just enough pressure in the tank to blow the contents out when the cock is opened As water is removed by the outgoing air blast, not by gravity, the cock can be positioned above the water line. For the same reason it probably doesn't matter if the outlet pipe protrudes a little inside the tank.

Dave

[not done it yetParticipant @notdoneityet]

Posted by Danny M2Z on 25/01/2021 11:59:01:

Posted by not done it yet on 24/01/2021 14:08:45:

When you look at some tanks the drain is not actually at the very bottom.

ndiy. I asked the same question a few years ago and never got a satisfactory answer but then the manufacturers must have a resun for this layout, Slill windering why?

I was not the initiator of that comment. I only replied. My reason for this was quite clear in my post, I thought?

[Mark RandParticipant @markrand96270]

I have an Ingersoll Rand (No relation ) automatic float operated drain system for my compressor. That would really need the drain to be at the bottom of the tank. The other problem with it at the moment, is that it's sitting on a shelf and not yet attached to said compressor!

[Gary WoodingParticipant @garywooding25363]

My new compressor arrived yesterday and obviously I want it to last a long time. It will seldom be used continuously for any length of time – mostly for just a few minutes, barely long enough for the pump to start up.

The instructions say to release the pressure and drain it every day after use, and this got me thinking. Suppose the tank is empty and I fill it. The pressure stretches the tank metal and water in the air enters the tank. Suppose 1cc of water is included for every tankful of air. I use, maybe, 1/4 of the tank contents, so 0.25cc more water gets in. Suppose now, that no more air is used for a week, say. What's best? To release the pressure and drain the water, then wait a week and refill with air, or to leave the tank full and empty it every 4 weeks, say?

If I drain each time, then 4cc of water passes through the tank, but if I drain every 4 weeks, then only 2cc of water gets in. Each time the tank is emptied and refilled, it goes through a stretch/release cycle, which can't be beneficial, and just draining the tank doesn't dry the surfaces – which remain damp. So what's best?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by not done it yet on 25/01/2021 13:33:49:

Posted by Danny M2Z on 25/01/2021 11:59:01:

Posted by not done it yet on 24/01/2021 14:08:45:

When you look at some tanks the drain is not actually at the very bottom.

ndiy. I asked the same question a few years ago and never got a satisfactory answer but then the manufacturers must have a resun for this layout, Slill windering why?

I was not the initiator of that comment. I only replied. My reason for this was quite clear in my post, I thought?

.

A clear demonstration of the fact that it is helpful to give attribution when you quote another.

I have never understood why some just pluck a few words, without that courtesy.

MichaelG.

[Sam Longley 1Participant @samlongley1]

Posted by Gary Wooding on 27/01/2021 08:10:35:

My new compressor arrived yesterday and obviously I want it to last a long time. It will seldom be used continuously for any length of time – mostly for just a few minutes, barely long enough for the pump to start up.

The instructions say to release the pressure and drain it every day after use, and this got me thinking. Suppose the tank is empty and I fill it. The pressure stretches the tank metal and water in the air enters the tank. Suppose 1cc of water is included for every tankful of air. I use, maybe, 1/4 of the tank contents, so 0.25cc more water gets in. Suppose now, that no more air is used for a week, say. What's best? To release the pressure and drain the water, then wait a week and refill with air, or to leave the tank full and empty it every 4 weeks, say?

If I drain each time, then 4cc of water passes through the tank, but if I drain every 4 weeks, then only 2cc of water gets in. Each time the tank is emptied and refilled, it goes through a stretch/release cycle, which can't be beneficial, and just draining the tank doesn't dry the surfaces – which remain damp. So what's best?

Have you considered removing the inspection cap & pouring in some thick oil, shaking the tank about a bit & letting that settle in the bottom? especially if the drain was not exactly at the bottom of the tank. Might help the air tools as well. It probably would not do any harm if a speck of oil blew out onto your lathe when blowing down either. no worse than moisture. But then I have a water trap unit for spraying.

[Mike PooleParticipant @mikepoole82104]

The oil will tend to float on the water so may not be as helpful as you would hope for.

Mike

[not done it yetParticipant @notdoneityet]

pouring in some thick oil

The thick oil will be blown out when the tank is drained? Best would be to arrange the tank vertically with the drain at the centre of the bottom dome – but beware of any drain sticking up inside the receiver.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Sam Longley 1 on 27/01/2021 08:42:42:

Posted by Gary Wooding on 27/01/2021 08:10:35:

…

Have you considered removing the inspection cap & pouring in some thick oil, shaking the tank about a bit & letting that settle in the bottom?…

Definitely wouldn't put oil of any sort in a compressor tank! It assumes 'thick oil' will never catch fire on it's own or slowly degrade into a vapour that might diesel or ignite due to static electricity. There's a lot of energy in oil. Rather than going off with a giant scary pop as being discussed in this thread, burning oil in the tank would result in a real explosion, more violent with flame.

Another problem, assuming the oil sticks at the bottom, is water would tend to concentrate at the oil/tank edge, causing a line of rust to consistently weaken the tank along a line.

And compressed air usually needs to be clean. Oil in the output is certainly bad for paint!

Dave

[Sam Longley 1Participant @samlongley1]

Posted by SillyOldDuffer on 27/01/2021 10:17:30:

Posted by Sam Longley 1 on 27/01/2021 08:42:42:

Posted by Gary Wooding on 27/01/2021 08:10:35:

…

Have you considered removing the inspection cap & pouring in some thick oil, shaking the tank about a bit & letting that settle in the bottom?…

Definitely wouldn't put oil of any sort in a compressor tank! It assumes 'thick oil' will never catch fire on it's own or slowly degrade into a vapour that might diesel or ignite due to static electricity. There's a lot of energy in oil. Rather than going off with a giant scary pop as being discussed in this thread, burning oil in the tank would result in a real explosion, more violent with flame.

Another problem, assuming the oil sticks at the bottom, is water would tend to concentrate at the oil/tank edge, causing a line of rust to consistently weaken the tank along a line.

And compressed air usually needs to be clean. Oil in the output is certainly bad for paint!

Dave

Oil seems to work OK in a car without exploding in the sump & steering etc!! Albeit at lower pressure, but quite hot, one assumes. We used to put it in my site compressors & it did no harm to them. I would have thought that it would have got flung round the inside of the tank & lined the inside. Only a suggestion for consideration.

Anyone doing paint jobs needs to use a condensation trap for starters, so that should not be an issue.

As for air being clean– Is there not a unit for injecting oil into the air line for tool lubrication? I am sure that my air bench presses had one on my window manufacturing line. Long time ago, so memory a bit faded.

Still have the water trap paint filter though.

 

Edited By Sam Longley 1 on 27/01/2021 12:29:09

[Nick WheelerParticipant @nickwheeler]

I wouldn't want oil in the compressor tank for all the reasons stated.

Oil in a sump isn't pressurised much, and doesn't have much oxygen to allow it to burn. That isn't the case in a tank of compressed air!

If used air tool oilers are fitted to the tool, after the airline connector. From what I've seen, most light users don't have them and rarely oil the tools manually.

[Jeff DaymanParticipant @jeffdayman43397]

Many pressure tanks for domestic water supply for wells, with a jet pump, here in Canada were hot dip galvanized in and out. These were rated to 75 or 100 psi continuous service. It would be a nice option to be able to buy a hot dip galvanized heavy gauge tank or a stainless heavy gauge tank air compressor. I would gladly pay a little more for those options. As well, automatic water drain valves as use on railway locomotive air brake air tanks here would be useful, and not a lot extra. (these are just a pneumatic time delay valve that exhausts a short burst at regular intervals.)

[old martParticipant @oldmart]

I would not recommend adding oil, that is one of the things that you want the air to be free of. Oiling rotary tools is a separate thing, downstream from the reciever. A shield between the compressor and the working area would direct the blast away from the operator if it was strong enough, but keeping the reciever in a separate area would be best, if possible.

Edited By old mart on 27/01/2021 16:10:19

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I don't know about an explosion risk of oil in your compressor, but if you want clean air, you won't put it in your tank. Air service units are very often used in industry, which very often include a regulator, a water trap and an oiler, most of them with a regulator that I've seen, have the regulator first, but some have it second, however the water trap is always before the oiler. It is quite likely that if you put oil in the tank, it will migrate out with the air flow over time and if you put a water trap in the air line, over time the oil will probably gunge the water trap up and then you may find a significant drop in air pressure and most likely volume available for your usage. Draining the water should be on a regular basis and automatic ones relieve you of having to do it.

On a job a workmate and myself, had to drain down a diesel tank and pipework. The tank was easy, but most of the pipework was in a narrow gulley in the floor of the building and there were also areas where the gulley was just between pipes under the floor. We could not just undo the pipework and let it into the gulley, as it was an open ended one that drained into a river and there was electric cabling in the gulley as well, (we were doing the job for the Environment Agency) so we came up with the idea of blowing the diesel out with compressed air and catching it in a container, but had a passing thought of combustion like in an engine as it was a very long pipe run of 1" black pipe, but we went for it anyway. The result was! the pipework was cleared of 20L or so of nice clean red diesel and no mess and no bangs.

Regards Nick.

[Gary WoodingParticipant @garywooding25363]

The instructions say to release the pressure and drain it every day after use, and this got me thinking. Suppose the tank is empty and I fill it. The pressure stretches the tank metal and water in the air enters the tank. Suppose 1cc of water is included for every tankful of air. I use, maybe, 1/4 of the tank contents, so 0.25cc more water gets in. Suppose now, that no more air is used for a week, say. What's best? To release the pressure and drain the water, then wait a week and refill with air, or to leave the tank full and empty it every 4 weeks, say?

If I drain each time, then 4cc of water passes through the tank, but if I drain every 4 weeks, then only 2cc of water gets in. Each time the tank is emptied and refilled, it goes through a stretch/release cycle, which can't be beneficial, and just draining the tank doesn't dry the surfaces – which remain damp. So what's best?

Doesn't anybody know the answer? Is it best to empty the tank after use, or just blow out the water with minimal loss of presure?

[Robert Atkinson 2Participant @robertatkinson2]

From fatique perspective it is always best to reduce the number of cycles (the very high pressure pure air bottles that were used for early thermal imagers had limited number of refills before being scrap). Most bursting failures of cheap tanks seem to be fatique related rather than corrosion which results in leaks.

As has been mentioned more water is added every stroke of the compressor so minimising that reduces how much water enters the tank

Overall best solution for a compressor used reguarly (more often than once or twice a week or the pressure does not leak away beween uses) is just drain the water and leave the tank pressurised. If it is only used infrequenty, drain it down and leave it empty. If in a warm dry location leave th drain valve open so it acually dries out.

Robert G8RPI

[Nicholas FarrParticipant @nicholasfarr14254]

Posted by Gary Wooding on 28/01/2021 15:35:47:

The instructions say to release the pressure and drain it every day after use, and this got me thinking. Suppose the tank is empty and I fill it. The pressure stretches the tank metal and water in the air enters the tank. Suppose 1cc of water is included for every tankful of air. I use, maybe, 1/4 of the tank contents, so 0.25cc more water gets in. Suppose now, that no more air is used for a week, say. What's best? To release the pressure and drain the water, then wait a week and refill with air, or to leave the tank full and empty it every 4 weeks, say?

If I drain each time, then 4cc of water passes through the tank, but if I drain every 4 weeks, then only 2cc of water gets in. Each time the tank is emptied and refilled, it goes through a stretch/release cycle, which can't be beneficial, and just draining the tank doesn't dry the surfaces – which remain damp. So what's best?

Doesn't anybody know the answer? Is it best to empty the tank after use, or just blow out the water with minimal loss of presure?

Hi Gary, well every thing you use has a stretch/release cycle one way or another, but everything is, or should be, designed to do this within the elastic range of the materials used, so you have to ask yourself if the manufacturers have got their sums right and do they leave any safety margin. Do you worry about the stretching/releasing cycles of your car fuel tank, (assuming you have a car that uses liquid fuel) OK it might not be as extreme, but fuel tanks aren't that thick, and you probably have emptied and filled it many more times, plus all the forces holding the fuel in, when the car is in use, or have done before the current situation we are all in. In the long run, everything has a finite useable life, but the hardest bit is to decide when you feel the need to replace or just don't need the things you have anymore.

Regards Nick.

[not done it yetParticipant @notdoneityet]

Looks more like GCHQ had been taking too much interest in this thread? The title has been changed to something less dramatic.🙂

Edited By not done it yet on 28/01/2021 19:39:31

[Martin KyteParticipant @martinkyte99762]

I had a compressor tank fail at work albeit a small bambi type. It failed at a weld where the tank brackets attatch to the frame. I estimate at around 60PSI. All I got was a loud pop and a hiss as it deflated. I suspect many are overthinking this and seeing disasters where there are none. I guess for large air receivers some more serious thinking needs to be done but compressed air stores a lot less energy than steam. If you are under 250 bar litres it doesn't officlally need inspection so I would assume the powers that be deem it intrinsically safe when it fails much like the lowest category steam boilers.

regards Martin

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