Air Compressor Warning

[Paul LousickParticipant @paullousick59116]

Another reason for releasing the pressure in the tank is relieve the stresses on the springs in the pressure relief valve and gauge. Leaving the springs in a compressed state can cause a permanent set and they will not return to their normal zero pressure position and could give a false reading. Releasing the pressure is also a recommended procedure when using welding gas regulators.

Paul.

[Chris CrewParticipant @chriscrew66644]

I have had a small Machine Mart 'Tiger' compressor in my workshop for the last thirty years, it is constantly switched on and fires up to replenish the reservoir as and when if I am blowing swarf off the machines or I occasionally drag it down the drive to reflate a car tyre. A few weeks ago it occurred to me to remove the drain plug on the bottom of the cylinder and, guess what? After thirty years constant use absolutely nothing came out, not a drop of water or anything else for that matter, so I replaced the drain plug and expect the compressor to be still going strong long after me!

[Mike PooleParticipant @mikepoole82104]

Have you checked there is no blockage of the vent?

Mike

[Gary WoodingParticipant @garywooding25363]

Posted by Chris Crew on 28/01/2021 23:26:24:

I have had a small Machine Mart 'Tiger' compressor in my workshop for the last thirty years, it is constantly switched on and fires up to replenish the reservoir as and when if I am blowing swarf off the machines or I occasionally drag it down the drive to reflate a car tyre. A few weeks ago it occurred to me to remove the drain plug on the bottom of the cylinder and, guess what? After thirty years constant use absolutely nothing came out, not a drop of water or anything else for that matter, so I replaced the drain plug and expect the compressor to be still going strong long after me!

Chris, read the first post in this thread.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Chris Crew on 28/01/2021 23:26:24:

… After thirty years constant use absolutely nothing came out, not a drop of water or anything else for that matter, so I replaced the drain plug and expect the compressor to be still going strong long after me!

So, what are we to make of this? The thread opens with a burst compressor tank:

And then Chris says his compressor is fine after 30 years of neglect and he expects it to last longer than him!

What's going on?

The problem is human beings are bad at assessing risk. Unless the consequences are bleeding obvious we don't get it! We understand it's unwise to sit in the bath with an electric fire balanced on our knees, but might reject the seriousness of Covid because the streets aren't littered with corpses. What virus, what problem?

And there are many risks where personal experience is almost irrelevant because the risk is statistical, only hurting a percentage. At least a thousand cases have to be analysed to understand what's going on. Smoking is a good example: comparing smokers with non-smokers by the million clearly shows – on average – that non-smokers live 10 years longer, while smokers are about 20 times more likely to die of cancer, bronchitis and emphysema, and 4 times more likely to die of heart disease. Whilst the statistics tell the awful truth, individual smokers don't see it. It takes years to do the damage, not everyone is affected, and we foolishly trust personal experience. This allows addicts to argue, 'My granny smoked 80 a day until she was run over by a tram aged 95' without realising the evidence is valueless unless compared with millions of other life experiences.

The range of possibilities often follows the bell curve of a normal distribution. This example is of academic performance. Given a year's worth of school-children, their exam results will look like this:

The same shaped curve likely covers the burst compressor and Chris's experience. The probability of a neglected compressor lasting 30 years is low and so also is the probability of tank bursting. Both are possible, but neither is likely. They are rare events on opposite sides of the curve, special cases. Most compressors sit in the middle: they aren't in good nick after 30 years, nor are they likely to spectacularly go pop during normal usage.

Owners can change their position under the curve for good and bad. Regular maintenance is good, but I suggest extending the life of an elderly compressor is asking for trouble. Designers know a great deal more than us, such as the type of steel used, calculated and actual burst pressures, the expected life of the equipment (in years and operating cycles), safety factors, corrosion resistance, and much else. Big difference between confidence and knowing. When it comes to safety it ain't smart to rely on luck!

Dave

 

Edited By SillyOldDuffer on 29/01/2021 10:38:38

[noel shelleyParticipant @noelshelley55608]

Gentlemen Please. This tread has on the one hand attracted far to much theory and on the other very little. It would appear that we nearly all seem to have a compressor of one size or other – how many have had a pin hole leak let alone a catastrophic shell failure ? Most safety is based on historic practical experience tempered with some theory and good practice(common sense). The issue of explosion due to THICK oil in the tank. The ignition of even a light oil at the pressures and temeratures we are talking about is not easy. Diesel fuel will not ignite until the temperature in the combustion camber is raised to about 800*C and the fuel finely atomised. When cold this process will often need the help of a glow plug to the get things started, so thick oil in a even warm tank is so unlikely to explode or ignite as to be on a par with a pig with wings !

There are many things that CAN go wrong, a blocked drain, a failed non return or unloader valve, a seized or stuck safety valve, the pressure control switch operating at the correct pressure. Then there's the motor?

The idea of a galvanized tank is good but one thought would be that it might instigate stress cracking due to the brittleness of the zinc/iron intermediate layer.

If you are reading this you have so far survived living with tis dangerous device ! Noel.

Edited By noel shelley on 29/01/2021 11:44:02

[Sam Longley 1Participant @samlongley1]

Posted by SillyOldDuffer on 29/01/2021 10:35:52:

Posted by Chris Crew on 28/01/2021 23:26:24:

Designers know a great deal more than us, such as the type of steel used, calculated and actual burst pressures, the expected life of the equipment (in years and operating cycles), safety factors, corrosion resistance, and much else. Big difference between confidence and knowing. When it comes to safety it ain't smart to rely on luck!

If designers know so much why do they not put an expiry limit on them then?

Perhaps it is because they do not know how the machine is going to be used. Only how they would LIKE it to be used.

So in that event they know nothing really.

Only the state of the machine when it leaves the manufacturer.

Which then comes to the point- If one looks after a machine it will last for years. Bit like one's body. If one abuses it ( by smoking, say) it can be expected to wear out prematurely. But if one opens the inspection bung every year or so & has a look inside for signs of rusting, drains it frequently, changes the compressor oil, Checks the safety valve etc. why should one not go on using it for years. In all likelyhood, with cheeps domestic compressors the first thing to fail will be the motor anyway. At that point scrap it.

I think that this thread is really over thinking the problem.

Risk, yes there is . But let's face it, with some products, who is to say it did not leave the factory with a fault & is likely to go bang in the first 2-3 hours?

[Dave HalfordParticipant @davehalford22513]

Lets face it, when compressor pumps wear out they start moving oil from the pump sump into the tank as well as blowing it out of the breather. The result is that creamy mayonaise like you used to get on engine oil filler caps back in the day. They don't ignite or the papers would have been full of it.

You stand a higher risk of a bang in a woodwork shop or Bakery with the wood dust and flour if it's allowed to get bad.

[David George 1Participant @davidgeorge1]

I had to run the air system at a medium factory of toolmakers and we had a writen scheme that was checked by the insurance company. The main compressors were a screw type and as such were listed as pressure vessels and were inspected by the insurance inspector every two years. The main receiver was inspected every year also by the insurance inspector and I had to remove the inspection cover so he could look at the inside to asses corrosion etc. The pressure relief valve had a handle to check it was working and was checked by me every month and by the insurance inspector every year by a test rig to check working pressure. The pipe work was galvanised steel pipe and as it was main three inch diamiter was also classed as a pressure vessel and was monthly checked by me and by the insurance inspector two yearly. This was logged and in a writen scheme which approved by a insurance inspector.

David

[SillyOldDufferModerator @sillyoldduffer]

Posted by Sam Longley 1 on 29/01/2021 11:45:57:

Posted by SillyOldDuffer on 29/01/2021 10:35:52:

Posted by Chris Crew on 28/01/2021 23:26:24:

Designers know a great deal more than us, such as the type of steel used, calculated and actual burst pressures, the expected life of the equipment (in years and operating cycles), safety factors, corrosion resistance, and much else. Big difference between confidence and knowing. When it comes to safety it ain't smart to rely on luck!

If designers know so much why do they not put an expiry limit on them then?

Perhaps it is because they do not know how the machine is going to be used. Only how they would LIKE it to be used.

So in that event they know nothing really.

…

No Sam, designers and builders always know much more than the owner! As far as I know Compressor Instructions never suggest putting oil or anything else in the tank to prevent corrosion. Nor do they mention fixing leaks by welding, brazing or Duck Tape. They simply recommend draining water at the end of each session.

Don't mistake what I'm saying. The evidence suggests ordinarily maintained compressor tanks don't explode. It also suggests tanks don't last for ever. Exactly as you say, 'At that point scrap it.'

Dave

[Graham StoppaniParticipant @grahamstoppani46499]

A heartfelt thanks to Gary. Because of this thread I checked my compressor yesterday…

Background

I bought this compressor in late 2016 from Aldi but the design is pretty generic so will apply to many other brands. To begin with I drained the tank regularly when in use and would get a thimble full of water each time. I then installed a dehumidifier in my workshop about a year ago and and around the same time the water I was getting out of the compressor reduced to a dribble each time I drained it. I became lax in checking the compressor as I assumed the dehumidifier was causing this. WRONG This is what I found yesterday:

1. Amount of water initially drained by removing the small drain plug

I gave the compressor a shake and could hear water sploshing around. I removed the large plug with a 17mm spanner and apart from a blob of crud nothing else came out. However, I could still hear water when I shook the compressor. I poked my finger up the drain hole and broke through a crust of muck that had formed there. This is what came out:

2. Third drainage attempt

3. over 150cc of rusty water

Following on from a comment made in an earlier post about checking the drain wasn't standing proud from the bottom of the air reservoir you can see in the next picture the drain plug's top two threads are discoloured. I read this as showing they have been standing proud from the bottom of the cylinder.

4. Drain plug threads and design

Conclusions

Because the water did not fully drain each time the compressor was checked it allowed crud to form over the drainage plug so that it eventually blocked the drain completely allowing a much larger volume of water to collect over time.

Solution

A couple of fibre washers added to the drain plug would lower it sufficiently to bring it level with the bottom of the inside of the air reservoir and stop the initial build up of water happening if drained regularly.

[not done it yetParticipant @notdoneityet]

Solution

A couple of fibre washers added to the drain plug would lower it sufficiently to bring it level with the bottom of the inside of the air reservoir and stop the initial build up of water happening if drained regularly.

Well done. Checked and rectified by a simple mod (could also have machined off the excess, instead, but washers are cheap). Apart from 4-5 years of potential rusting already caused by poor manufacturing and lack of regular drainage, that should certainly lengthen the safe lifespan of your compressor (although I suspect the pump will wear out first if used quite often).

My receiver is well over-sized for my present usage (I no longer do grit blasting) but I always open the drain valve and allow the tank to blow itself empty, after use.

[Sam Longley 1Participant @samlongley1]

Posted by Graham Stoppani on 30/01/2021 06:44:17:

A heartfelt thanks to Gary. Because of this thread I checked my compressor yesterday…

Mid quote deleted for clarity

Conclusions

Because the water did not fully drain each time the compressor was checked it allowed crud to form over the drainage plug so that it eventually blocked the drain completely allowing a much larger volume of water to collect over time.

Did it go "Bang"?

[Tony Pratt 1Participant @tonypratt1]

I also drained my compressor for the 1st time in many years & about 100 ml of whitish water came out. My question to the chemists amongst us, will a tank rust more with standing water as opposed to only moist air being cycled in & out?

Tony

[Anthony KendallParticipant @anthonykendall53479]

Now everyone has had a fair crack about reservoirs, is anyone else concerned about the quality of the output fittings on most of the available new compressors?

Having had a pressure switch failure, I removed the whole assembly from the reservoir, breaking a casting in the process. This enabled me to examine it – the body was made of what some call muck metal and it was pretty easy to prize off pipes branching from the main stem, at the joints.
Looking for a replacement, I found the whole assembly, including switch, two gauges, regulator and the tree all ready to screw into the reservoir, all for about 12 quid delivered – they are all over the net!
Having looked at what came off, the switch looks reasonable quality, but the remainder seemed just crap.

All that said, I decided to use a new switch and mount it using decent fittings. Probably, if the switch had not failed, the whole lot might have carried on forever – as long as I had not caught anything on it!

[not done it yetParticipant @notdoneityet]

Posted by Tony Pratt 1 on 30/01/2021 09:08:53:

I also drained my compressor for the 1st time in many years & about 100 ml of whitish water came out. My question to the chemists amongst us, will a tank rust more with standing water as opposed to only moist air being cycled in & out?

Tony

Iron requires water and oxygen to rust. Steel rusts away faster than cast irons. Rusting takes place more quickly at warmer temperatures. All simple facts that are easily verified/demonstrated

All simple experiments, carried out at school, 60 years ago. Nails in a dry glass container, wire nails with water and air and another with the nails under boiled water with a thick layer of oil added to prevent any air dissolving (that was before the make-up of air was considered). Only the wire nails with both air and water present rusted (to any degree).

Cast iron machine tools are more easily recovered than mild steel tools which are allowed to get wet.

Any protective surface coating will be effective to prevent rusting – while it remains intact.

An example I always used to explain to my bosses, for why I was ordering rust resistant grinding media (at twice the price of chopped steel rod). The cheap grinding media, if used dry, needed a much lower replenishment rate than when wet grinding – where any surface corrosion was immediately scrubbed off by the grinding process thereby providing a new reactive surface, so wear was caused by corrosion, more than by the grinding process

The same process will occur in a steel tank as when chemically blueing or blacking steel surfaces – the chemical is insufficient on its own – it needs an initial oiling which permanently fills the pores – to make it effective.

The same occurs with aluminium (which is quite reactive) – the surface soon oxidises after manufacture or is ‘anodised’ to form an impervious surface layer of aluminium oxide, making further corrosion less likely. It does not work forever and once that hard layer is removed, the aluminium might corrode quite quickly (goes white on the surface).

There are quite a few factors to contend with, to avoid/reduce these metals from corroding in air. Also (cheaper) lower quality products can rust faster (think of some makes of car back in the last century which were called rust buckets?)

Best practice is to avoid air and water contact with bare steel surfaces. One is OK, together is not OK.

Edited By not done it yet on 30/01/2021 10:02:24

[pgk pgkParticipant @pgkpgk17461]

My Surgery's Bambi dental compressor was subject to pressure vessel regs and regularly inspected. The pressure vessel went about 10-12 years before being condemned and replaced. That didn't have a ventral drain but did have an external clear water trap we drained daily (sprung valve at bottom) – presumably a dip tube to bottom of pressure vessel forced all condensate out…. quite a nice solution compared to my cheapr hobby and farm compressors here where you have to remember to drain them and fiddle undeneath.

pgk

[SillyOldDufferModerator @sillyoldduffer]

Posted by Sam Longley 1 on 30/01/2021 08:44:28:

Posted by Graham Stoppani on 30/01/2021 06:44:17:

…

Conclusions

Because the water did not fully drain each time the compressor was checked it allowed crud to form over the drainage plug so that it eventually blocked the drain completely allowing a much larger volume of water to collect over time.

Did it go "Bang"?

This one did:

[Sam Longley 1Participant @samlongley1]

Posted by SillyOldDuffer on 30/01/2021 10:09:31:

Posted by Sam Longley 1 on 30/01/2021 08:44:28:

Posted by Graham Stoppani on 30/01/2021 06:44:17:

…

Conclusions

Because the water did not fully drain each time the compressor was checked it allowed crud to form over the drainage plug so that it eventually blocked the drain completely allowing a much larger volume of water to collect over time.

Did it go "Bang"?

This one did:

 

And there we go again– back to the one in 10 million that was probably as rusty on the outside as much as it was on the inside & most people with any sense would have already said "Hey this is beginning to look a bit dodgy, perhaps we should have a look inside, or think about a new one"

Edited By Sam Longley 1 on 30/01/2021 11:45:04

[not done it yetParticipant @notdoneityet]

perhaps we should have a look inside, or think about a new one"

Have you checked yours? It is usually an event which happens to other people. It is unlikely the next one will be yours. But it does happen to someone. Are you a ‘someone’ or a ‘nobody’. Yours could be the next one.

Everybody, Anybody, Somebody and Nobody. There is a poem on these 4. Have a look at it:

**LINK**

[Ex contributorParticipant @mgnbuk]

perhaps we should have a look inside

USB endoscope cameras can be obtained from Ebay from £5-8 delivered depending on cable length. The camera head includes a ring on variable intensity Leds. Removing the end cap from the receiver will allow access. Aldi & Lidl occasionally sell self-contained endoscopes with an integrated colour display with similar functionality for £30-40. So the equipment to conduct a simple internal visual inspection need not be too costly.

Ultrasonic thinkness testers can be obtained from the same source from around £70 if you want to emulate the professional air installation inspection process & check that the shell has a constant thickness in areas showing surface rust. A non-intrusive test conducted from outside the receiver.

Our annual air installation takes place on the 8th Feb. I don't anticipate that the report will differ much from the last 14 I have been party to – it will state that the inside of the receiver shows surface rust, but that the ultrasonic test shows an even shell thickness in excess of that required for a receiver of it's size. That vertical receiver is fed by a 7.5Kw screw compressor, lives outside & is drained 2-3 times a day to prevent condenate build up.

Nigel B.

[Dave HalfordParticipant @davehalford22513]

Posted by Tony Pratt 1 on 30/01/2021 09:08:53:

I also drained my compressor for the 1st time in many years & about 100 ml of whitish water came out. My question to the chemists amongst us, will a tank rust more with standing water as opposed to only moist air being cycled in & out?

Tony

That's a little bit of oil in the condensate.

[Sam Longley 1Participant @samlongley1]

Posted by not done it yet on 30/01/2021 13:37:51:

perhaps we should have a look inside, or think about a new one"

Have you checked yours? It is usually an event which happens to other people. It is unlikely the next one will be yours. But it does happen to someone. Are you a ‘someone’ or a ‘nobody’. Yours could be the next one.

 

Well actually I have checked i,t because I have had several large site compressors which were tested annually as well as a few in my work shops. As a result they were always tested & H & S training always taught me to check.

When I retired I took a small one home & in 2015, after 5 years I decided to change it for a new one to be safe. I removed the bung both ends, rolled it on its side & shone a torch in. It did not look clean. So that was it.

So in spite of comments one does take care. But I do not get in to the realms of exploding oil & welding parts & some of the theories posted. Just stick to sensible use & there will be no problem. Of course it is wise to highlight the issue on the forum; but some do get a bit carried away.

 

 

Edited By Sam Longley 1 on 30/01/2021 15:38:18

[Robert Atkinson 2Participant @robertatkinson2]

Posted by SillyOldDuffer on 30/01/2021 10:09:31:

Posted by Sam Longley 1 on 30/01/2021 08:44:28:

Posted by Graham Stoppani on 30/01/2021 06:44:17:

…

Conclusions

Because the water did not fully drain each time the compressor was checked it allowed crud to form over the drainage plug so that it eventually blocked the drain completely allowing a much larger volume of water to collect over time.

Did it go "Bang"?

This one did:

 

Sam said " And there we go again– back to the one in 10 million that was probably as rusty on the outside as much as it was on the inside & most people with any sense would have already said "Hey this is beginning to look a bit dodgy, perhaps we should have a look inside, or think about a new one" "

As has been said before, that tank failed from fatigue at the longitudinal weld. Look at the photo. Corrosion may have had some contribution, but not from rusting through.

Edited By Robert Atkinson 2 on 30/01/2021 17:28:24

[Anthony KendallParticipant @anthonykendall53479]

Posted by Sam Longley 1 on 30/01/2021 15:34:14:
…. Of course it is wise to highlight the issue on the forum; but some do get a bit carried away.

Perish the thought!

[Author]

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