Burrell "Thetford Town" Boiler test

[Nigel Bennett]

I've been asked to look at a 2" scale Burrell Showman's Engine of Ronald Clark's design.

The engine has been out of use since about 1988.

As a preliminary, before conducting a proper test, I pumped it up with a hand pump and I got it to 50psi or so, but there seemed to be a bit of leakage past the regulator. On a traction engine, of course, the cylinder casting forms part of the pressure vessel and the regulator is mounted on top of this. What do other Boiler Testers do when faced with with this situation? Blanking off the regulator as in normal railway locomotives is not so straightforward in a traction engine. I imagine it might be possible to make up some kind of plate to replace the safety valve mounting and possibly put some jointing under the regulator valve, holding it all in place with a pressure screw in the plate, but it does seem a bit of a bother to have to go to.

Does anybody know what the working pressure is of Thetford Town? I imagine it would be 80psi or so, but the pressure gauge fitted only reads up to 100, so it may be a little less, especially as it's a "double high" rather than a compound. Don't suppose anybody's got a set of drawings going cheap?

Thanks for any help anybody can offer.

[ejparrott]

I've got a set of drawings, I'll look them up tomorrow. I think the boiler is 100psi by design.

Usually steam comes straight up from the barrel into the regulator chamber below the safety valves. Most common method of sealing is to remove the safety valve assembly, and fit a plug into this hole

[Nigel Bennett]

Thanks, Ed; if it's a pluggable hole for the steam feed into the regulator chest (rather than a cored cast hole), that would make things easier.

[ejparrott]

Damn, forgot! Will try to remember in the morning!

It's not a cored hole, it's not very big either.

[ejparrott]

Right, remembered at last!!

I have the original Clarke boiler drawing which shows a working pressure of 120PSI, great for a compound engine. The replacement Reeves/Piddington drawing shows 80psi - that'll never compound. In my opinion, the replacement boiler is good for 100PSI no problem. It's 1/8"/3mm copper plates, and stays at 3/4" square pitch will have no problems containing that.

The cylinder block question is a bit more difficult. The original block as designed has lots of proper cores in it, and the steam rises around the nearside or LP side of the block. The new way of doing it involves a casting which has no cores in it at all, and there is now a replacement top cover which is bolted to the block. The steam for this version is through the offside or HP side of the block, with a series of 1/4" holes drilled and plugged through the steam chest walls and around up to the top....dreadful design. If you need me to post pictures I can.

[Nigel Bennett]

Thanks for looking it up, Ed; it seems that I'd better just take off the safety valve plate and have a look at what's underneath - I've no idea which version it is. As the pressure gauge only read up to 100, I can't imagine it was ever worked at 120. Whether it was built for 120 is another question!

Since you've offered, a picture would be helpful if it isn't a bother.

Thank you.

[ejparrott]

I can do that, I'll get the drawings and the camera out later

[Nigel Bennett]

Ed - if you haven't got round to digging out the drawings, you needn't. The Burrell's owner has managed to track down some drawings, so all will be revealed.

Thanks. Nigel

[ejparrott]

No worries! I have the 2 reeves updated drawings if they're not in his set