Small steam engine

That sounds rather better than the pop-off method that I read about.

Is there a good UK source for lots of little compression springs? All I've seen are those kits in the likes of Machine Mart, which seem to be mostly expansion springs.

-- Wally

Things are always clearer in the cold, post-upload light.

Car tyre valves have a little compression spring in them. Your local tyre fitter throws dozens away each day. (You only want the core). They might even be rustproof.

Martin L

Noted for the pressure thingy. In the main, though, I'm looking for springs that will go round M5 and M6 screws.

-- Wally

Things are always clearer in the cold, post-upload light.

With regard to safety valves, they are designed with a " pop off" action.

with a pop off as the valve starts to open it exposes a larger area to the pressure, forcing the valve to open further, and not allowing it to re seat until a significant reduction on pressure has been achieved... a very desirable characteristic in the case of safety valves.

Proper safety valves have locked settings and a way to test they are operating correctly. ( in commercial practice the settings are sealed with a lock or lead seal, and may only be set by "authorised agents " ).

I'm not sure at what sizes boilers and pressure vessels come under the full regulations when a proper safety valve becomes mandatory, anyone have these figures ?

-- Jonathan

Barnes's theorem; for every foolproof device there is a fool greater than the proof.

To reply remove AT

Wally

Send me your address and I'll let you have a copy of the instructions for a kit that we make. I'm not suggesting you buy the kit but I can supply the materials and further details for you to make your own if you're interested.

Mine wasn't very noisy when I ran it by blowing! grin

Wally it really is fairly simple to make a spring that would serve your requirement. Just wind some piano wire around a former a little smaller diameter than you want! You could be techie and soften it first then reharden and temper it. Cost is negligable and you can start with a small guage first for a softer spring. Personally I think a lever operated deadweight safety valve is pretty good and of course easy to adjust as well. But obviously to use one of these the boiler must be secure as tipping a weighted valve could reult in unexpected releases of water. I noticed an earlier poster referring to the dnagers of steam and hot water. In my experience steam is pretty safe almost as as soon as it escapes as it cools almost instantly and contains little heat anyway. Water on the other hand is contains rather a lot of heat and doesnt expand and cool on its way out so nasty scalds can be expected. THis by the way is why the so called steam cleaners are actually hot water cleaners! ChrisR

The pop-off I'm referring to was described on a web page about a small oscillating engine. It consists of a bit of brake pipe in the line carrying the steam, and has a short length of rubber tube fitted to it. The tube is a snug fit to the brake pipe and the other end is plugged. The idea is that the friction in the fit is sufficient to withstand a given amount of pressure, which can be varying by altering how far the tube is pushed onto the pipe. If the pressure gets too high, the tube pops off and the pressure is relieved. A bit like those safety things on pressure cookers.

Not sure I can visualise how a larger area is exposed. Are you describing the type with a ball and spring?

-- Wally

Things are always clearer in the cold, post-upload light.

I'm afraid there is something called "latent heat of vapourisation" that contradicts what you are saying

Heat capacity of water 4.2J per gram per degree Celsius Latent heat of vapourisation 2300J per gram.

So if you cool 1g of water from 100 down to 37 it loses

264.6J If you condense 1g of steam on your hand it loses 2300J, about 8.6 times as much. (Plus the 264 if your hand doesn't heat up)

Martin L

think of a conical seat for a valve, when it's closed the pressure is on the central holes area, when it lifts the pressure is on the whole of the valves face area.

-- Jonathan

Barnes's theorem; for every foolproof device there is a fool greater than the proof.

To reply remove AT

I'll keep this in mind. Rather than hunt down piano wire, I bit the bullet today and bought an assortment pack of springs. I had found an industrial supplier who was charging about 10p per spring, so the Draper 7 quid box of

200 (1/3 compression, 2/3 extension) was deemed to be good enough value.

Indeed.

-- Wally

Things are always clearer in the cold, post-upload light.

Should I be visualising a countersunk hole with a conical valve pushed into it by a spring? :-)

-- Wally

Things are always clearer in the cold, post-upload light.

Well, my little design is coming along, but I'd be interested in taking a look at the instructions nonetheless - tonal at blueyonder dot co dot uk. Thanks.

-- Wally

Things are always clearer in the cold, post-upload light.

That would work but...

Send me an E-Mail I can post to if you would like an adobe file which includes a cross section of a valve seat and other details of safety valves ( 1.4 Mb file ).

-- Jonathan

Barnes's theorem; for every foolproof device there is a fool greater than the proof.

To reply remove AT