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Compressor inspection

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Jonathan David09/06/2020 01:01:19
2 forum posts

I have a small 25ltr compressor that gets used 2 or 3 times a week, I drain it weekly (when I remember)

but its now 12 years old, I was staring to think it may need inspecting?

not done it yet09/06/2020 07:41:28
4872 forum posts
18 photos

Endoscope type camera? Or just pressure test it?

Hopper09/06/2020 07:54:06
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4768 forum posts
104 photos

I wouldn't bother. If it ever corrodes all the way through you'll hear a loud hissing noise and that's about it. Its not a steam boiler.

There are millions of those cheap compressors in use around the world and nobody inspects them. Seems to work ok.

Edited By Hopper on 09/06/2020 08:25:41

Jonathan David09/06/2020 08:30:03
2 forum posts

That's what I thought, but I made the mistake of googling it!

Hopper09/06/2020 08:47:38
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4768 forum posts
104 photos

Sounds like you already made your mind up. Buy a new compressor if you want to be totally safe. Or pay an inspection service to send over a qualified person who knows what they are looking at to to scope it and certify it.

Or do what every one else does and drain it regularly and carry on. Make sure compressor is angled so condensate runs downhill to the drain cock end.

Edited By Hopper on 09/06/2020 08:50:37

Adrian R209/06/2020 08:50:29
33 forum posts
5 photos

I've got one of these which is puzzling me. It's supposed to be 150psi but labours to get up to this pressure and then as soon as it does the safety valve blows and depressurises before the compressor cuts out. I thought the cutout switch was defective so removed it but when tested with a high pressure cycle pump it seems to work as intended (NC, opens at around 150psi, closes again at 120psi).

My current plan is to derate the cut out switch to a 120/90 equivalent, are there any better ideas?

Adrian

Chris Evans 609/06/2020 09:02:33
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1724 forum posts
Posted by Adrian R2 on 09/06/2020 08:50:29:

I've got one of these which is puzzling me. It's supposed to be 150psi but labours to get up to this pressure and then as soon as it does the safety valve blows and depressurises before the compressor cuts out. I thought the cutout switch was defective so removed it but when tested with a high pressure cycle pump it seems to work as intended (NC, opens at around 150psi, closes again at 120psi).

My current plan is to derate the cut out switch to a 120/90 equivalent, are there any better ideas?

Adrian

Mine did that until I replaced the casting that carries the two gauges and air outlets. About £11 for the new casting /gauges/pressure switch. It now holds pressure for days. Take a look on eBay for compressor spares.

Danny M2Z09/06/2020 09:31:33
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892 forum posts
283 photos

I asked this question many years ago but don't recall getting a satisfactory explanation.

Why is the compressor drain valve located about 10° off from the bottom?

I have to tilt my el cheapo compressor to get the last sputters of water out from the valve.

Obviously there is a good manufacturing/scientific reason for this but it escapes my logic ;-}

* Danny M *

mgnbuk09/06/2020 09:43:07
792 forum posts
61 photos

Our compressed air installations at work have to be inspected annually - including a 50 litre Clarke portable compressor. There is a calculation - system volume x working pressure in Bar IIRC - and inspection is mandatory in a working environment if the calculation result exceeds a certain number. The 50 litre receiver 8 Bar Clarke compressor exceeded the number & had to be inspected.

The receiver inspections are basically an endosope internal inspection through an end cap / inspection port + an ultrasonic shell wall thickness test + safety valve test & overall visual inspection. The main workshop receiver at work is very large (3 metres tall) and lives outside un-protected - I have been working here for 14 years, this receiver was second hand when it was purchased at around the time I started and it has not had any advisories on any of the inspections in that time. It is more heavily built than a DIY portable type, but is used 8 hours a day 6 days a week for 50 weeks a year.

We use an external specialist company Mandate Systems for our inspections. You could do most of their inspection regime yourself - USB endoscope cameras are really cheap now for a look through one of the receiver end plugs. It would be the ultrasonic shell thickness test that would require equipment not usually in a home workshop. I doubt, though, that you would find much amiss.

Nigel B.

Brian Oldford09/06/2020 09:45:10
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683 forum posts
18 photos
Posted by Danny M2Z on 09/06/2020 09:31:33:

I asked this question many years ago but don't recall getting a satisfactory explanation.

Why is the compressor drain valve located about 10° off from the bottom?

I have to tilt my el cheapo compressor to get the last sputters of water out from the valve.

Obviously there is a good manufacturing/scientific reason for this but it escapes my logic ;-}

* Danny M *

Easy of manufacture maybe?

Adrian R209/06/2020 10:01:33
33 forum posts
5 photos
Posted by Chris Evans 6 on 09/06/2020 09:02:33:

Mine did that until I replaced the casting that carries the two gauges and air outlets. About £11 for the new casting /gauges/pressure switch. It now holds pressure for days. Take a look on eBay for compressor spares.

Not the same arrangement as mine unfortunately, the pressure switch is a separate component rather than being combined with the gauges etc. We're talking about this beastie, the offending switch being an SK-0810.

https://www.sipuk.co.uk/sip-06236-airmate-tn-1-5-25-o-oil-free-air-compressor-230v.html

Adrian

Paul Lousick09/06/2020 10:25:25
1493 forum posts
568 photos

Drain probably 10° from the bottom because it is easier and cheaper to do it this way.

Paul

Grindstone Cowboy09/06/2020 14:52:30
325 forum posts
27 photos

Never really understood the reasoning behind horizontal cylinders - I have a (very old) vertically configured Ingersoll-Rand compressor, takes up very little floor space and everything drains out the bottom with no issues. Doesn't look like it is any harder to make them that way rather than horizontal.

Rob

old mart09/06/2020 15:45:09
1906 forum posts
151 photos

When I installed the three phase compressor at the museum, I dumped the drain valve and ran a hose inside the building to an easily accessible ball valve, and ran the rest of the hose back outside. The draining is so easy now that it gets done every time the compressor is shut down. The compressor inspector from the insurance company told me that receivers normally fail at a rusty weld and leak without exploding like a high pressure vessel could.

not done it yet09/06/2020 16:10:30
4872 forum posts
18 photos

We use an external specialist company

Likely far cheaper to buy another receiver than pay out for a specialist company.

If it is a ‘buzz-box’ it is surprising that it is still going strong if used so regularly over that period - you must have looked after it well? They (the chinese) don’t make long-lived pumps at the cheaper end of the market. A good quality pump is another matter. Is yours a belt driven or direct coupled pump?

Brian Sweeting09/06/2020 19:07:44
437 forum posts
1 photos
Posted by Adrian R2 on 09/06/2020 08:50:29:

I've got one of these which is puzzling me. It's supposed to be 150psi but labours to get up to this pressure and then as soon as it does the safety valve blows and depressurises before the compressor cuts out. I thought the cutout switch was defective so removed it but when tested with a high pressure cycle pump it seems to work as intended (NC, opens at around 150psi, closes again at 120psi).

My current plan is to derate the cut out switch to a 120/90 equivalent, are there any better ideas?

Adrian

Sounds more likely that the pressure relief valve needs replacing as it is out of calibration.

not done it yet09/06/2020 21:41:44
4872 forum posts
18 photos

Sounds more likely that the pressure relief valve needs replacing as it is out of calibration.

There is always the possibility of a pressure gauge which is under reporting and a pressure switch that has been adjusted too high? Might explain why the machine labours to get the receiver up to pressure?

Robert Atkinson 209/06/2020 22:12:45
avatar
751 forum posts
17 photos
Posted by mgnbuk on 09/06/2020 09:43:07:

Our compressed air installations at work have to be inspected annually - including a 50 litre Clarke portable compressor. There is a calculation - system volume x working pressure in Bar IIRC - and inspection is mandatory in a working environment if the calculation result exceeds a certain number. The 50 litre receiver 8 Bar Clarke compressor exceeded the number & had to be inspected.

<SNIP>

Nigel B.

The regulations on pressure equipment at work apply when the product of pressure and volume exceeds 250 Bar Litres. So a 250litre receiver has to be inspected if it operates at more than 1 bar at 10 Bar (~150PSI) 25 litres an above have to be inspected.
There are a couple of notable exceptions, no test mandated below 1 Bar (gauge i.e differential to local ambient) regardless of volume and all steam equipment has to be inspected regardless of volume.

Robert G8RPI

mgnbuk10/06/2020 08:11:00
792 forum posts
61 photos

Likely far cheaper to buy another receiver than pay out for a specialist company.

Probably, though the annual inspection cost isn't as much as you might expect. IIRC less than £500 for the site visit (a couple of hours ) + the certification.

They (the chinese) don’t make long-lived pumps at the cheaper end of the market.

The Clarke small "hobby" type compressors I have used were Italian made. In my experience they are well made & last almost indefinately if the oil is changed occasionally & the inlet air filter is present. The "oil free" type are pretty useless, though - very low duty cycle & short life if this is exceeded.

Nigel B

Adrian R210/06/2020 09:03:37
33 forum posts
5 photos
Posted by not done it yet on 09/06/2020 21:41:44:

Sounds more likely that the pressure relief valve needs replacing as it is out of calibration.

There is always the possibility of a pressure gauge which is under reporting and a pressure switch that has been adjusted too high? Might explain why the machine labours to get the receiver up to pressure?

Pressure switch is a sealed unit, no adjustments possible. Gauge could be under reporting, not tested that. Safety I would have expected to fail low rather than high as it's a spring and that would be how one ought to work (?!)

I suspect it labours because it's a cheapo oil free unit - cylinder head gets pretty hot and you can hear the beat change as it runs up so presumably some expansion going on that reduces efficiency. TBH I would love to junk it and get one of the silent fridge motor types but they are expensive and it is rarely used so not a priority for expenditure, just a bit of a puzzle.

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