Compressor inspection

[Jonathan DavidParticipant @jonathandavid14814]

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?

[Jonathan DavidParticipant @jonathandavid14814]

[not done it yetParticipant @notdoneityet]

Endoscope type camera? Or just pressure test it?

[HopperParticipant @hopper]

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 DavidParticipant @jonathandavid14814]

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

[HopperParticipant @hopper]

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 R2Participant @adrianr2]

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 6Participant @chrisevans6]

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 M2ZParticipant @dannym2z]

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 *

[Ex contributorParticipant @mgnbuk]

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 OldfordParticipant @brianoldford70365]

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 R2Participant @adrianr2]

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 LousickParticipant @paullousick59116]

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

Paul

[Grindstone CowboyParticipant @grindstonecowboy]

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 martParticipant @oldmart]

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 yetParticipant @notdoneityet]

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 Sweeting 2Participant @briansweeting2]

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 yetParticipant @notdoneityet]

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 2Participant @robertatkinson2]

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

[Ex contributorParticipant @mgnbuk]

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 R2Participant @adrianr2]

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.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Paul Lousick on 09/06/2020 10:25:25:

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

Paul

More likely it's to stop wet muck settling in the outlet pipe and valve. If there's enough pressure in the tank when it's blown down, any water just below the valve should be pushed out provided the outlet is clear. I always think of Goldfinger leaving the aircraft…

Dave

[duncan webster 1Participant @duncanwebster1]

A long way down the to-do list is to fit a solenoid valve to the drain so that when you unplug the compressor it depressurises the tank and blows out any water. As I said it's a long way down the list!

[Brian MorehenParticipant @brianmorehen85290]

I came across this a few years ago when working on steam boilers and chemical distillation units which did require a yeary test certificate as do air compressors over 25 ltr capacity, Inspectors answer was a air tank of this size will leak and if the safety valve blows before you can do anything the air has gone . A boiler is much the same but somone could get burnt or scolded with steam , a Steam operated still is much the same if they blow inside the jacket the risk is mixed with the chemical being stilled.if the outer skin goes someone may get scalded. This is why compressors are only tested above 25 Ltr. This may have changed in the last 10 yrs .Did appear in a court case where i stated that the compressors did not have a test certicate, Answer dismiss this compressor and its value.

Hope this answers your question on compressors…

Regards Brian

i

[jimmy bParticipant @jimmyb]

I had the same thoughts a few years ago about my 16 year old cheapie.

As has been said, it'll just leak when its knackered.

If you are worried, just replace it.

Jim

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