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Air Compressor Warning

The bomb in the workshop (retitled to encourage air compressor owners to read this thread)

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Sam Longley 129/01/2021 11:45:57
939 forum posts
34 photos
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 Halford29/01/2021 12:09:08
2007 forum posts
23 photos

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 129/01/2021 17:58:55
avatar
1808 forum posts
503 photos

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

SillyOldDuffer29/01/2021 18:23:38
Moderator
8491 forum posts
1891 photos
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 Stoppani30/01/2021 06:44:17
avatar
120 forum posts
26 photos

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

20210129_131750.jpg

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

20210129_132021.jpg

3. over 150cc of rusty water

20210129_132341.jpg

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

20210129_132057.jpg

20210129_132438.jpg

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 yet30/01/2021 07:44:48
6734 forum posts
20 photos

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 130/01/2021 08:44:28
939 forum posts
34 photos
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 130/01/2021 09:08:53
1930 forum posts
12 photos

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 Kendall30/01/2021 09:47:52
152 forum posts

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 yet30/01/2021 09:58:59
6734 forum posts
20 photos
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 pgk30/01/2021 10:02:00
2552 forum posts
293 photos

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

SillyOldDuffer30/01/2021 10:09:31
Moderator
8491 forum posts
1891 photos
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:

burst.jpg

Sam Longley 130/01/2021 11:41:40
939 forum posts
34 photos
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:

burst.jpg

 

And there we go again-- back to the one in 10 million cryingthat 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 yet30/01/2021 13:37:51
6734 forum posts
20 photos

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**

mgnbuk30/01/2021 14:12:28
1176 forum posts
71 photos

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 Halford30/01/2021 14:28:26
2007 forum posts
23 photos
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 130/01/2021 15:34:14
939 forum posts
34 photos
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 230/01/2021 17:26:06
avatar
1195 forum posts
20 photos
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:

burst.jpg

 

Sam said " And there we go again-- back to the one in 10 million cryingthat 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 Kendall31/01/2021 09:07:51
152 forum posts
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!

Jeff Austin 131/01/2021 19:04:42
11 forum posts

Air receivers should be inspected periodically, obviously not enforced for diy types but a good idea nevertheless,

I have only ever seen the aftermath of one air receiver that exploded and it did explode, it was some years ago and being used in a medium sized car repair garage, the vessel in question was a vertical one stood at the side of a compressor that was feeding into it, this was in the bad old days of piston compressors that were all air cooled and consequently when worked hard they ran at high temperature and as a consequence there was lots of oil carry over as the piston clearances went miles out due to heat, the consequence of all this was that the oil that had accumulated in the vessel actually ignited and the pressure rise was so rapid that the pressure relief valve was rendered useless, the result was literally an explosion, the vessel ripped apart and punched a hole through the floor above,

This is why you should be careful using compressed air and compressors, keep them in good condition and inspect the vessel yourself periodically, the chance of catastrophic failure is very small but you do not want to be around if it happens, the picture of the small veseel that looks like it has peeled open should be enough to warn of the potential for injury to anyone stood near,

Vessels are inspected and can have a retest requested if the condition has worsened, testing is done with water for the simple reason that any failure when pressurised with liquid is far less dangerous due to physics, you cannot compress a liquid so there is very little stored energy, when you compress a gas you are storing energy so when it is released it is all that energy that will harm you,

as always look after your tools and they will look after you

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