Making a small boiler

[robin]

I'm thinking of making an espresso machine, which will need a brass boiler of approx 4" diameter, capable of handling, say, 4 bar. Are boilers normally bored out of solid bar (wasteful) or formed from a tube with brazed ends? Where can you buy such tubes from?

[gwrfan]

Hi Robin,

Boilers used by Model Engineers are usually made from seamless copper tube, which is available from ME suppliers, such as Reeves 2000 and Blackgates Engineering. The ends are usually silver soldered into position (along with the various smaller diameter internal tubes, etc). Such boilers are usually steamed at up to 100 PSI (more or less). I'm not sure where you could obtain brass tubing of 4 inch diameter, and if brass is necessary, then you may have to have a piece of suitable gauge (thickness) brass sheet rolled and silver soldered. Having said all this, it's not just a simple job, and you would need to have your design 'approved' by someone who knows what they are doing, especially if you intend to have said boiler in a public place, such as a cafe.

I rather expect that some of our more expert technicians here will offer better guidance than I can.

Regards

Geoff

[Tim Bayliss]

Robin,
Forget the boiler - I reckon this could well be an application for 'flash steam'.
What do you think, Lads?
Tim.

[jackrae]

Have just had a look at a commercial unit and it seems to run at about 15PSI (1 barg)

Normally one wouldn't recommend brass for pressure containers since it degrades - see previous correspondence re old style brass blow-lamps. If using an alloy rather than copper you should be going for gun metal or bronze.

I believe you need to pass water over the beans rather than steam - the steam being the motive force pushing the "superheated" water through the grind. At 1 Barg the temperature would be about 120 degrees centigrade.

An interesting project though - how do you intend heating the boiler and controlling the pressure. I can just imagine the fun of brewing up after dinner with a coal fired boiler and a little turbine driven grinder and steam powered perculator. Ah for the aroma of a freshly brewed coffee complemented by the smell of steam oil and coal smoke.

[robin]

Was planning on using an electric element - but I like your thinking!!!
I've been drinking too much espresso and reading www.coffeegeek.com but thought I'd give it a go, as this guy did:

www.espresso-restorations.com/P1.html

[jackbaynes]

Hi Robin, Read with interest your intention to build a small boiler and where to find a tube
about 4" diameter. Try Ebay under collectables, trench art. You will find quite a few old artillary
shellcases of various sizes, they are made of brass about 18"long and heavy duty, they are tapered slightly but might fit the bill for you. I got one recently for £5.
regards jackbaynes

[Tel]

A shell rolled from sheet & close rivetted would look super-smick on a project like that. Gives you a much wider choice of material thickness as well.

[robin]

How would you go around sealing the seam, or can you rivet that tightly?

[Tel]

Well, yes, you can get it tight with rivets, although I think I'd 'caulk' it with a light silver soldering. Even soft solder would do.

[robin]

Just won a stand on eBay for my lathe so can start making some swarf fairly soon!!!