BSP adaptor for an Air Bottle?

[jon.p.weaver]

One of my most used tools in the garage is my compressor as an air blower. But I keep thinking how much I would like a portable version.. SOmething like a "Recharable Air Blower" which I could fill from my compressor.

As an ex-diver, I had an idea.. I have a small (perhaps 1/2l) air bottle and I figured that with the correct fittings, I could connect it to my cylinder and fill it. As my project developed, I realised that if I fitted a standard 'quick release' fitting to the top of the bottle. I could use it to power ANY tool.. Obviously its not going to give much air, but certainly enough to drive in a few staples for example.

The idea is sound, but trying to get the fittings has proved impossible.

The thread in the bottle is 7/10" (not sure if 7/10" is right, but thats what my calipers say it is) but no-one that I have found stocks anyhting like this, which will convert to BSP.. Once its in a BSP thread, I already have plenty of adaptors which will let me hook it up.

So, the question is, can I get a adaptor to convert the thread on the bottle to BSP?

If not, where could I get a small bottle (

[Roger Mills]

What would normally screw into your gas bottle? Can you get a fitting with the right thread onto which you could braze a short length of copper pipe, with a BSP fitting at the other end?

[Tom Woods]

you could use a fire extinguiser bottle. sometimes available from scrap merchants i gather. That will probably have a sensible sized thread on it already. The one hanging on the wall in my office at work looks very similar to the fittings on my pub gas co2 bottle (which are avaialble from welding suppliers).

[jon.p.weaver]

Its an interesting idea and something that I have thought about.. Its a steal valve, which connects to a full sized dive bottle.. But there are a number of reasons why I don't want to do this.

1. Its steel, so brazing to copper is almost certainly not going to work.
2. It means destroying a perfectly good valve
3. Its got a TINY hold through it (I guess because its designed to work at 232bar, so volume isn't an issue). Obviously I could drill this out to make it bigger.

But it is an option should I not be able to locate a source for the correct parts! My other option is to obtain an old Fire-extinguisher bottle. But again, I don't know wheere I would be able to connect a standard BSP thread to it.

Jon

[Andy Dingley]

Do the maths. You can't do this for workshop pressures and store a useful amount of energy in a bottle small enough to be portable. For anything smaller than a zeppelin, you get two nails and it's flattened again.

Your dive bottle is designed for a squillion psi. Like all HP air systems outside submarines, it only needs a moderate mass airflow and so the passageways are deliberately designed to be tiny. If you did use it, you wouldn't get enough volume airflow out of it to drive an air tool.

If you use a dive bottle anywhere around its design pressure, you need to design a HP air system. You're on your own there!

If you even use a dive bottle there are problems. Just turning it into a plantpot involves paperwork that makes CORGI look like Blue Peter. You have to destroy the cylinder by the official protocol (making sure you don't turn you and your bandsaw into a small sticky mess when it turns out to have still had pressure in it). You're also _really_ prohibited from modifying SCBA kit - if you do anything with it, you first have to "de-mil" it and make it entirely certain it can't ever be confused again with use for its original purpose. Then there's the legal aspect of getting your arse sued off by angry cylinder companies.... (DAMHIKT)

I only know of one guy who I'd regard as competent (legally and technically) to dispose of a SCBA cylinder appropriately, and certainly none of the divers (the cave divers are beyond hope anyway). And that's picked from a circle of people with fairly fearsome attitudes to what's possible in a shed.

In practical terms, compressed gas just ain't going to work (unless you're back to squillion psi). If you _must_, then you need to store liquid instead. More stored mass means more stored energy. CO2 is practical here, for small values of practical.

Also a SCBA cylinder is the wrong thing (and a dive bottle is, I understand, even worse). You can't get the volume airflow out of it. There's another obvious source though, pub CO2 cylinders.

[jon.p.weaver]

wouldn't get enough volume airflow out of it to drive an

I think that you completely missed my point.. My compressor holds 100L at 8 bar.. I know from experinece that even a 25L will hold enough air to do a fair amount of work between charges.

My idea is simply to charge a dive cylinder to 8bar so that I have a VERY small amount of air, which is mobile.. I realise that I am not going to get much out of it, but figured that for my needs (i.e a few second of puff, or an odd staple) it might work.

I realise that a Dive Cylinder is high pressure (232 or 300bar to be exact), and thats why its got a very tiny hold in the value... .But I am simply talking about using it for an 8 bar application!

I have actually taken the valve out and now have an threaded opening in the top of the cylinder which is approx 7/10" wide.

As I said, I am not expecting much. 1/2L of air at 8 bar is going to give me almost nothing.. But it should be enough for what I want. As I said< i am not expecting to hget hours of air.. Nor even minutes or perhaps even seconds.. But I should simply be able to blow something out of it.

Jon

[rocky]

[AJH]

Exactly the same on the one attached to my mig welder ;-)

AJH

[AJH]

I often charge my cheap compressor reservoir up and take it to work, it's got enough puff to blow out the dust from a tractor radiator and saves humping a 4kVA generator along to run it. Secret is to make sure there are no leaks and screw the pressure regulator right out.

My mate informs me that two pub CO2 bottles filled with compressed air at 120PSI fill up his front tractor tyres from flat, didn't make much impression on my tractor though.

AJH

[Tom Woods]

Thats what i meant! ;)

[jon.p.weaver]

Well. I have to say.. You were right :(

I managed to find a supplier of 'adaptors' and after shelling out =A36 for a couple of parts to convert my bottle thread to one suitable to fit my quick fit connector. I assembled the puzzle of parts with copious amount of PTFE and connected it to my compressor.

I opened the tap, heard the air going in, removed it and connected my air blower tool.. When I pulled the trigger, I litterally got a single PUFF!! Nothing more than a long breath of air blown from your mouth.

I was clearly wrong about this.. A 1/2L bottle is not nearly big enough to give any amount of air worth talking about.

My decision now is simply to scrap the idea as stupid, or seek out a slightly larger bottle (perhasp 2L+) and try again!

Jon

[adder1969]

I'm sure I've seen what look more like 2L divers emergency air bottles and they must contain more than a long breath of air.

[Clive George]

.5L at 8 bars is 4 litres. Aka "bugger all".

Even 2L won't give you that much. 8 bar is just too low pressure.

cheers, clive

[Andy Dingley]

Do the maths.

If you really have to, do it by experiment. Fill your compressor tank and switch off. Then use that until it's empty. Divide that by the capacity of that tank over the capacity of your portable tank.

There's a _reason_ why SCBA kit needs to run at a squillion psi.

[Tom Woods]

I would be tempted to go for this approach.

as an idea of price. I've bought a pub co2 bottle for my mig welder (from a welding shop). It cost about £45 for a full bottle and all the required regulators and pipework (more regulators than you probably need since i can adjust the flow rate and i dont think a sodastream would need to - you can possibly just get away with the on/off tap built into the top of the gas bottle). It now costs me £12.50 to get the bottle refilled with 4.5kg or so of gas.

[Adrian]

That sounds like a very cost-effective way of buying gas.....

I've got a vague recollection of seeing somewhere on the net (possibly in the States) where they sold a length of pipe with a 'sodastream' valve on the end of it - the other end to connect to a high capacity gas bottle.... must try & remember where that was !

Thanks Adrian

[AJH]

A little ambiguity there I think, I don't have a pub CO2 bottle on my mig

AJH

[R]

I saw that idea.....Google Paintball gun gas etc