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PYRTE Traction engine build nearing completion, but basic question

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Ken Ratcliffe13/08/2020 19:53:54
11 forum posts

Hi All,

About a year ago now I asked for help with silver soldering a boiler as I was starting a PYRTE steam engine - my first attempt at a steam engine. Well, it is nearing completion, almost all done but I haven't tested if my boiler holds pressure. Why ? I didn't think I would get this far, so never really worried, it would make a good garden ornament, but now - I WANT TO SEE IT RUN - so, I was initially wanting to use a car tyre foot pump to check for leaks, but what seems simple - I am can I connect a tyre pump to the back of my boiler - where I have 1/4" x 40 bushes - or any other suggestions.

JasonB13/08/2020 20:01:00
18628 forum posts
2048 photos
1 articles

If you must use an air pump then first fill to the brim with water and then pump it up as it will be a lot safer if things go wrong. ideally use a hydralic pump to pump water in to bring it upto pressure ( 2 x working)

Just turn a simple male/male adaptor with 1/4 x 40tpi one end and something similar to a car valve the other, you could just do a series of fine grooves if you don't want to cut a thread.

pgk pgk13/08/2020 20:20:22
1887 forum posts
288 photos

When i pressure tested my boiler (which leaked like a proverbial sieve) - I bummed an old inner tube locally, cut out the valve stem, cleaned the rubber off and epoxy glued it into a simple adapter I made to fit a bushing.

To reinforce Jason's comment - fill the boiler full with water before pumping air to see the leaks...


Nigel Graham 213/08/2020 23:43:16
720 forum posts
16 photos

With great respect to Jason and Pgk Pgk, I will amplify and clarify...

It is normal practice to pressure-test any pressure-vessel first with water only, not water and air as Pgk's advice might be read.

This is because if it does fail, it won't rupture explosively as it could with air (or worse, hot water and steam under pressure, because that hold even more energy.

Once you are satisfied it is safe under the test over-pressure as Jason says, you steam-test it to working pressure only, no higher,. for two reasons.

- To verify the safety-valves work correctly and discharge all the surplus steam the boiler can generate, at the design pressure. (It is common to have to adjust them in that initial test to the design pressure.).

- To verify the boiler feed arrangements work as they should.

Now, you don't tell us what boiler feeds your engine has, and I don't know the PYRTE design beyond some sample photos on-line, but a traction-engine normally has a feed-pump driven from the crankshaft, and an injector; and a miniature might have a hand-pump as well as or instead of the injector.

Either pump can be used for the hydraulic test - if it's the engine-driven one just put the drive out of gear and turn the flywheel by hand. Note that any leak past the regulator will fill the valve-chest and cylinder with water, to their dismay, so keep the cylinder drain-cocks open.


NB: I say "you steam-test it..." For your initial test, and all at own risk if you are only driving it around your own garden, but for insured public running you don't, not as the engine's owner, though I don't know which country you are in so can only speak for UK practice.

It would need a formal test for such running...

Probably most of us here on this site belong to model-engineering societies linked to several federations operating a single UK-wide boiler-test regime for miniature engines. The boiler-testers are club-members working to instructions agreed with the insurers and HSE... and they can't test their own engines either! Nor are they, or the clubs, allowed to charge for it but you are usually expected to be a full member.

If you have it tested professionally you pay commercial rates, of course, and things can be tricky if you try to mix and match commercial and society-federation test regimes.

Anyway, Good Luck with this engine, and might we see pictures of you driving it in due course?

Hopper14/08/2020 00:49:13
4768 forum posts
104 photos

Your domestic mains water supply is usually somewhere about 80 psi so could be hooked up to provide a water only pressure test. I guess ideally throttle supply through a valve (tap) to limit flow in event of a leak. Pressure could be controlled by a bleed off valve between the throttling valve and the boiler. Would be enough to locate any initial leaks at least. 

Edited By Hopper on 14/08/2020 00:51:02

Ken Ratcliffe14/08/2020 08:50:07
11 forum posts

Thanks all - I suspect mine will also leak like a sieve - the build-book starts with the boiler, perhaps the most difficult silver soldering part for a complete novice. It does hold water without leaks (not under pressure, which is a start.

Good point on water to see leaks, I was going to submerse it and look for air bubbles

Cuttings threads is no problem, but won't the coupling need a non return valve to pump it up......could be me being dim here, it not then I am good to go - is there where the inner tube valve comes in ?

For now I will be doing nothing more than getting it running in the garden.....MAYBE if that is successful I may take it out and would get it steam tested professionally first.

Pictures...…..sure, but don't all hold your breathe, the speed I go would make PYRTE look fast !

Harry Wilkes14/08/2020 09:06:41
963 forum posts
63 photos

Hi Ken

There's a post on the Traction Talk forum about using the engines own hand pump for the hydraulic test, maybe you could do the same. link


Howard Lewis15/08/2020 13:26:35
3536 forum posts
2 photos

A boiler (even a small one ) that fails with steam at full working pressure is dangerous. Not only is there the risk of flying metal, but the steam being above atmospheric pressure will contain even more energy and be at a temperature well over the normal ( 1 atmosphere ) 100'C temperature. At 100'C it takes 536 calories to turn a gramme of water (Almost 7 x the quantity need to raise the water from 20'C to 100'C )into steam,hence it scalds when it condenses!

Superheated steam will strip flesh.

When things return to normal, if you join a M E Club, there are usually regular, (Often pre season ) boiler tests which which will qualify you for insurance when running in the presence of the public.

BUT, unless you want to be most unpopular, don't just join for the boiler test; participate in club activities!


vic francis15/08/2020 13:57:44
52 forum posts
7 photos

Hi Ken , look at Keith Appletons superb videos on boiler testing , much easier than words! On utube ;

pm sent!

kind regards


Edited By vic francis on 15/08/2020 13:59:08

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