DIY full size air compressor - am I mad?

[LunarOne]

Easternlight said:

Just for your information. BSP and NPT pipe threads are dimensioned by the pipe bore diameter, which is why they are larger than you'd think.

Thanks, that makes sense now - kind of!

[ruggedscotty]

Gary C said:

Super Sonic said:

"full size"? I once worked on a building site putting diesel in stuff and the compressors were up to portakabin size.

Well, if you want to play that game

Our air systems at work use 4 3m x 3m receivers then into two 20m long by 4m diameter receivers from 6 oil free screw compressors, and thats just the instrument air.

Each of the eight diesel engine start systems use 3 reciprocating compressors and 4 1m x 3m receivers then the general service air system uses four more big (2 are portakabin size) screw compressors and 3m x 3m receivers.

Thats 34 compressors in all with a huge reservoir of air to keep essential systems running if we loose site supplies.

Then the 50 or so fire systems each have their own compressors to run the air detection for dry deluge valves.

And then we have the Forced Air Compressor system. This compressor runs off a 3.3kV motor and has a four stage centrifugal compressor with wheels the size of big dinner plates. Only runs up to about 14 bar but the CFM is huge and is used to purge the reactor of CO2 and fast cool the turbine if we want to work on it as soon as possible after a trip.

Then there are the various hydrovane and test compressors around the site.

Edited by Gary C on Saturday 7th August 14:06

safe to say you won with this one.... thats some set up

[LunarOne]

mikey k said:

I manage a compressed air company, there are a few things I'd point out from your post;
1) if that receiver drain was blocked there may well be internal corrosion, I'd want to look inside and check it. (a commercial user has to inspect it every 24 months and insure it against failure if it is over 250 bar litres ie more than 25 litres at 10 bar)

Thanks so much for your thoughts Mikey!

I don't have one of those inspection cameras and if I did, I'm not sure what it would tell me. Most of what came out of the bottom was oil rather than water, which I'm glad about. Maybe I should pour in some rust treatment and let it sit in there before letting it squirt out the bottom vent?

mikey k said:

2) for a machine that size we never bother fitting any sort of auto drain, simply put a large ball valve on there and manually drain it regularly. The rust and sediment in that will block most drains very quickly.

That's my plan!

mikey k said:

3) That receiver should have a safety relief valve on it. For your safety I would replace it with a new 11 bar one.

It does have a safety release valve. It vents if I pull on it, but I don't know at what pressure it would vent by itself. It's definitely above 11.5 bar though as it doesn't vent before the compressor finished charging air.

mikey k said:

4) Surprised to see the pressure control is determined by current draw, normally there is a mechanical pressure switch that breaks the circuit at the pressure you set.

Perhaps I wasn't clear, but the pressure switch is triggered by pressure. However the relay also contains a current-limiting breaker in the relay. Before I swapped the breaker for a higher capacity one, the breaker was tripping and physically moving the power switch to "off". Now with the new relay, the current isn't tripping it out and the switch shuts off the motor when the compressor reaches the correct pressure. But it then doesn't move the physical switch from "auto", so the motor can restart automatically when the pressure drops. In other words the pressure switch controls the pressure normally by switching power to the motor as necessary. But if there is an overcurrent condition, the switch is tripped to off and the compressor will not run again without physical intervention. In addition to all this, the motor itself has its own current-limiting breaker in the circuit fitted in the black box above it.

mikey k said:

5) Keep a close eye on the pully alignment and belt tension, if either go out you will eat belts

Check.

mikey k said:

6) This thing will muller your electric bill.

I actually don't think it will given that I'll use it only occasionally. It draws less than 10A when the receiver is full and much less when it isn't. It goes from 1 bar to 10.5 bar in just a few minutes, and once pressurised it goes from 8 bar to 10 bar in about 30 seconds. Even though it's a big unit, it doesn't use up as much space as you might think, so I can justify having it as a home/DIY unit. While I'd like to spray with it and use blasting media occasionally, most of my usage will come from more standard air tools like a die grinder, cutoff tool, ratchets and most frequently of all, my blow gun, tyre inflator and staple gun which I use for shoemaking. The staple gun doesn't need very much air at all and could run from a 10L hobby compressor. But I like the idea of having a proper compressor even if it's only occasionally. I assume there's no harm in leaving it pressurised long term, and only letting it run when I need air. After a few days it doesn't seem to have lost much pressure if at all, so in a way, it's much less likely to annoy my neighbours than my little compressor which runs its motor after just a few seconds of use. I can use this for ages without needing to run the motor. I doubt I'll even notice any difference to my electricity bill, especially if I keep leaks to a minimum!

[mikey k]

ruggedscotty said:

Gary C said:

Super Sonic said:

"full size"? I once worked on a building site putting diesel in stuff and the compressors were up to portakabin size.

Well, if you want to play that game

Our air systems at work use 4 3m x 3m receivers then into two 20m long by 4m diameter receivers from 6 oil free screw compressors, and thats just the instrument air.

Each of the eight diesel engine start systems use 3 reciprocating compressors and 4 1m x 3m receivers then the general service air system uses four more big (2 are portakabin size) screw compressors and 3m x 3m receivers.

Thats 34 compressors in all with a huge reservoir of air to keep essential systems running if we loose site supplies.

Then the 50 or so fire systems each have their own compressors to run the air detection for dry deluge valves.

And then we have the Forced Air Compressor system. This compressor runs off a 3.3kV motor and has a four stage centrifugal compressor with wheels the size of big dinner plates. Only runs up to about 14 bar but the CFM is huge and is used to purge the reactor of CO2 and fast cool the turbine if we want to work on it as soon as possible after a trip.

Then there are the various hydrovane and test compressors around the site.

Edited by Gary C on Saturday 7th August 14:06

safe to say you won with this one.... thats some set up

Not the largest but up there

Land Rover Solihull is larger with over 5MW of compressor motors!

[mikey k]

LunarOne said:

I actually don't think it will given that I'll use it only occasionally. It draws less than 10A when the receiver is full and much less when it isn't. It goes from 1 bar to 10.5 bar in just a few minutes, and once pressurised it goes from 8 bar to 10 bar in about 30 seconds. Even though it's a big unit, it doesn't use up as much space as you might think, so I can justify having it as a home/DIY unit. While I'd like to spray with it and use blasting media occasionally, most of my usage will come from more standard air tools like a die grinder, cutoff tool, ratchets and most frequently of all, my blow gun, tyre inflator and staple gun which I use for shoemaking. The staple gun doesn't need very much air at all and could run from a 10L hobby compressor. But I like the idea of having a proper compressor even if it's only occasionally. I assume there's no harm in leaving it pressurised long term, and only letting it run when I need air. After a few days it doesn't seem to have lost much pressure if at all, so in a way, it's much less likely to annoy my neighbours than my little compressor which runs its motor after just a few seconds of use. I can use this for ages without needing to run the motor. I doubt I'll even notice any difference to my electricity bill, especially if I keep leaks to a minimum!

80% of the input power is waste heat so they are VERY inefficient, that was more my point. If you can do the job with an electric tool it will be far cheaper.
At 18p/kWh (typical domestic rate) it will cost you 64.8p/hour it runs.
You WILL need to dry the air for spraying or shot blasting, every compressor generates wet air, basic physics. You will get away with it on air tools that don't mind a bit of water.
Just be aware and consider the volume of stored energy and fuel for a fire with a receiver always being pressurised.

[LunarOne]

I've now added a 1/4" ball valve to the bottom outlet so that I can manually drain water from the receiver. I'd ordered a PCL ATC12 1/2" filter and regulator from an Amazon seller, but it hasn't turned up and the vendor claims that Royal Mail has lost it.

So now I need to order again. I'm thinking of lubrication again as I do want to use some tools which need it. But PCL say you can't switch off lubrication with their combined ATCFRL12 product, so I'm thinking of getting the filter/regulator and lubricator separately. and connecting them in such a way that I can use a Y-valve to bypass the lubricator when necessary. I'm sure I could daisy-chain them if necessary with quick couplers or just buy inline oilers, but in true PH style I'm looking for the most professional solution for no apparent reason. I would mount these on a piece of board on my garage wall. The only issue is finding short (0.5M-1M) lengths of air hose with threads to plumb everything together. I guess I could do it with metal pipework too, but water in the air could cause unwanted corrosion that would be difficult to detect and harder to fix than with flexible rubber/plastic hoses or pipes.

Here's my proposed arrangement. Any comments?

[mikey k]

Simpler way
regulator
T piece with ball valve/PCL for non lubricated take off
Lubricator
ball valve/PCL take off for lubricated air

[LunarOne]

mikey k said:

Simpler way
regulator
T piece with ball valve/PCL for non lubricated take off
Lubricator
ball valve/PCL take off for lubricated air

I guess the real difference is that your way allows me to have both lubricated and unlubricated air in use at the same time, while my method means I don't have to disconnect hoses to change between lubricated and unlubricated air.

My next question - apart from paint spraying which you've already told me needs dry air anyhow, are there any applications which NEED unlubricated air? Will the tiny amounts of oil in the air cause problems when inflating tyres? I'd have thought that tyres come into contact with enough oils that it's not damaging to the rubber.

[InitialDave]

LunarOne said:

My next question - apart from paint spraying which you've already told me needs dry air anyhow, are there any applications which NEED unlubricated air? Will the tiny amounts of oil in the air cause problems when inflating tyres? I'd have thought that tyres come into contact with enough oils that it's not damaging to the rubber.

Media blasting, plasma cutting.

Edited by InitialDave on Wednesday 8th September 15:30

[LunarOne]

InitialDave said:

LunarOne said:

My next question - apart from paint spraying which you've already told me needs dry air anyhow, are there any applications which NEED unlubricated air? Will the tiny amounts of oil in the air cause problems when inflating tyres? I'd have thought that tyres come into contact with enough oils that it's not damaging to the rubber.

Media blasting, TIG welding, plasma cutting.

TIG welding? I've done a lot of research into that as I'd love to learn how to do it (we did MIG welding in my school days) but never heard of it being used in the process, except to use with a die grinder/descaler. I know compressed air is used for plasma cutting, thanks to Andrew Camarata's Youtube channel.

Media blasting is something I definitely plan to do, so I'd better plan on unlubricated air then.

[InitialDave]

LunarOne said:

TIG welding? I've done a lot of research into that as I'd love to learn how to do it (we did MIG welding in my school days) but never heard of it being used in the process, except to use with a die grinder/descaler.
That was me having a brain fat from a parallel discussion with my mate about his garage setup, disregard!

[hidetheelephants]

Lubricators are a waste of money unless you're running an assembly line; just squirt a bit of oil in the quick release fitting before hooking it up if it's something that needs lube.

[dhutch]

LunarOne said:

my method means I don't have to disconnect hoses to change between lubricated and unlubricated air.

Not so, because you will need different hoses anyway, because the hoses used with the lubricator with become oily inside!

[dhutch]

hidetheelephants said:

Lubricators are a waste of money unless you're running an assembly line; just squirt a bit of oil in the quick release fitting before hooking it up if it's something that needs lube.

Also this.

[LunarOne]

So I'm after a bit more help on my 150L Clarke Air vertical compressor that I've converted to single phase. A couple of weeks ago, it started spewing air from under the pressure switch, but only when the motor was running. When the motor stops, it seems to hold air in the receiver. Thinking that it was the safety valve, I ordered a replacement (the new one came without a pull ring) and fitted it, but it hasn't made any difference. This evening I needed to use a rotary wire brush to clean up a few parts so I fired up the compressor and had a more detailed look at the problem.

There's a small diameter metal pipe which emerges from under the pressure switch, secured with two brass fittings. I think this pipe feeds receiver air pressure into the pressure switch. Anyway, the uppermost brass fitting has a hole in it (red arrow in picture) and it's through this hole that the air is escaping. When I put my finger over the hole, it stops. But it also stops when the motor isn't running, so the receiver stays charged. However this large air leak means the receiver cannot be charged up to its nominal pressure - it maxes out at about 70psi before it leaks as much air as the compressor is delivering.

So why is this hole there? Is it some sort of check valve? Why did it suddenly start leaking now? Any ideas much appreciated.



Also, I owe you an update. I know you all said not to bother with an oiler, but as I was mounting the filter/regulator on a board, it seemed like very little extra expense and work to add an oiler and be done with it. I may add a 90-degree elbow so that the oiled air outlet so that the hose can hang vertically.

[Novexx]

The leak from below the pressure switch is coming from the unloader valve (Condor EV3 or EV3i), the valve will be fooked & require replacement.

The unloader valve is (well, should be) closed while the motor is running & open when it's not, it unloads pressure from the pump side to allow an easier start for the motor when it starts with a semi charged receiver.

Edited by Novexx on Tuesday 21st December 19:40

[LunarOne]

Novexx said:

The leak from below the pressure switch is coming from the unloader valve (Condor EV3 or EV3i), the valve will be fooked & require replacement.

The unloader valve is (well, should be) closed while the motor is running & open when it's not, it unloads pressure from the pump side to allow an easier start for the motor when it starts with a semi charged receiver.

Thank you! Now I know what it is, I've ordered a replacement for a few pounds.

[hidetheelephants]

I can't be bothered rereading the thread, but don't use a hose that's had lubricated compressed air through it to spray paint with; guess how I know this? You appear to already know this as you've got an outlet between the water trap and the lubricator, but it's worth restating if it saves someone else from making the same error.

[Krikkit]

hidetheelephants said:

Lubricators are a waste of money unless you're running an assembly line; just squirt a bit of oil in the quick release fitting before hooking it up if it's something that needs lube.

Definitely this, then all your hoses and fittings are clean too, no headaches.

[LunarOne]

hidetheelephants said:

I can't be bothered rereading the thread, but don't use a hose that's had lubricated compressed air through it to spray paint with; guess how I know this? You appear to already know this as you've got an outlet between the water trap and the lubricator, but it's worth restating if it saves someone else from making the same error.

Krikkit said:

hidetheelephants said:

Lubricators are a waste of money unless you're running an assembly line; just squirt a bit of oil in the quick release fitting before hooking it up if it's something that needs lube.

Definitely this, then all your hoses and fittings are clean too, no headaches.

Thanks yes it's been said. But since all my air tools so far (with the exception of the blow gun and the tyre inflator) need to be oiled, I figured I'd prefer to have it at source. I'm not planning on spray painting but I'm aware that oil in the air will wreck it. But as my air isn't dried, I don't think it's suitable for paint spraying anyway. I would like to get a sandblasting cabinet at some point in the future, and that doesn't want oil in the line either. But air hose is so cheap that it's no bother to have separate hoses for oil and no oil applications.