Compressor Air Receiver

I built a compressor years ago from a fridge motor and a large propane cylinder, almost silent, loads of air for normal use. The large propane cylinders are lying about near any pikey site, there is one in the public field near me (ESSEX). The tap can be easily unscrewed and replaced with a screwed iron fitting, from which you could attach anything, I would suggest you just use it as an auxiliary receiver with a flexible hose linking it to your main compressor tank, obviously you will need high pressure hose and a couple of quarter turn valves, but these are cheap and easily available from an industrial hose stockist.

mrcheerful

In the past I've used a tractor tyre coupled in to the system to act as a reservoir. I suppose a car tyre would do. Watch the pressures though. I expect your compressor goes up to 100 - 120 psi and I don't think I'd like to put much more than 60 psi into a car tyre.

I know this is advice after the event, but when buying a compressor it's important to compare its air delivery with the air consumption of any tools you might want to use. Short bursts of a high air consumption tool are OK if you've got a reasonable air reservoir, but if you're going to use the tool continuously the compressor itself must deliver the appropriate quantity of air into the tank to keep it topped up. Having more tank capacity - as you are trying to arrange - does not really cure the problem because the compressor has to work for ages trying to fill up this larger tank. Might you not be better to sell your new compressor and buy one of the right size, putting the cost of the operation down to experience?

Rob Graham

Mr Cheerful - Funny, outside work there are works going on and I just noticed a few propane cylinders (47KGs) which look perfect....where can I get hold of one of these? Preferably empty and free! Or is it just a case of being lucky and finding one and half-inching it.

Are there any laws I should think about to owning a tank like this in my garage? Even tho it will not be filled with propane, just air?

Rob - You are probably right, but I am not in a situation to be able to afford to just get rid and buy bigger. Wish I was. I don't mind how long it takes to fill...I am just hoping that once the larger capacity is full, it wil take much longer to discharge. ie get longer bursts of pressure before running out and themotor kicking in almost instantly.

Cheers for your replies.

Jon

To add to this....where could I simply buy an empty bottle?

If you're a commercial business it needs pressure testing for safety every five years. They have a tendency to rust through from the inside.

If you keep looking you'll find an old 125litre tanked compressor, probably 3phase going for peanuts on ebay.

Go to a scrapyard and get an air tank off a lorry. As big as possible. It will have fittings which may be BSP, or may be NPT, the American standard, esp. if it's from a ford cargo. Also get a pocket full of fittings/hose etc.

Connect it up so the compressor fills it's own tank and the new one, take your supply from the new one. Once it's full, the gaps in use will help to keep the pressure up. It won't be as good as one with the right tank to start with, but it will be an improvement.

Steve

OK, so in my personal garage there's no issues to owning one? Especially seeing as I am only going to use it for air, not gas. So if it did start to leak it would only be air.

Ta

Good idea. Will have to have a look around, as I can't think of a scrappy off top of my head that has lorries. Must be around tho.

Cheers

The safety check re rusting is not because it will leak, the worry is that it can go off with the explosive power of a small bomb, sending chunks of thick steel in all directions. Personally, I do not think there is too much to worry about in your situation, but you should look inside every once in a while in case it has gone very rusty, a water drain off tap at the lowest point is a good idea too.

mrcheerful

If you want air tools to behave like electric ones, you need a compressor with a suitable output. Increasing the tank size will only help if they're used intermittently - and then as you've found - a too small compressor will have to run for longer times than the tool is in use to make up the deficit.

Why not simply use electric ones?

They don't leak, they explode! 25 litre receivers at 10 bar are the largest you're allowed without inspection, above this they're considered dangerous & need testing . As with anything , common sense will avoid disaster.

In the case of die grinders , my electric die grinders far far bigger than my pneumatic one. & it cost more, ditto for the metal nibbler & the staple guns & nailers.

I have a 47kg propane cylinder hooked upto my 50litre 2hp compressor which is excellant for 'bolstering' the compressors output when i am spraying or using the blow gun for extended periods. The motor does fire up fairly soon when drawing air and runs continuously, but with the hugely increased volume available, i'm able to maintain 80psi at the spraygun for much longer periods. Obviously eventually it does run down, and the motor takes a good while to recharge it, but that usually co-incides with refilling the paint cup :)

Tim..

What pressure do these go up to? I can see a big bang here one day.

Rob Graham

Unlikely IMHO. Commercial vehicle systems tend to be around 10-12 bar, his small compressor is unlikely to exceed this, and his safety valve will still operate.

Big bangs are unlikely at these kinds of use. Diving cylinders are filled to 300 bar or thereabouts.

Steve

Well it seems the 47kg propane bottle is the way to go....now where to find one...

Im sure I could buy one new off a gas supplier but I imagine that would be expensive. Would rather find one lying in someone's garage not being used anymore :-)

Anyone happen to have one?

Because you can't use them in the rain, and you can't take them with you in the lorry and use them at breakdowns. Of course you could if they were cordless, but then they tend either to be underpowered or hideously expensive.

Horses for courses.

Steve

Well, they *can*, but you'd have an extremely rare event on your hands if it did. The pressure involved is unlikely to be above 10 bar with his small compressor, and if it was to rust through from inside as has been suggested, by far the most likely scenario would be for it to fail to build up pressure one Monday morning after a weekend standing idle, accompanied by a hissing noise as the compressor tried to keep pace with the leak.

Explosive failures are far more the province of gas cylinders and diving cylinders where 300 bar pressure is common.

Cue ludicrously exaggerated stories of catastrophe from people who have had several workshops destroyed by a cylinder the size of a baked bean tin, along with families wiped out, thousands of people made homeless etc.

Steve