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7 1/4G Edward Thomas

rmb5241

Joined: 1-01-70

Topics: 3

Replies: 4

Posted: Tue 1st Nov 2011, 2:25pm
7 1/4G Edward Thomas

Has anyone built one of these to the drawings supplied by Reeves 2000?

Any practical tips/advice would be much appreciated.

Has construction been documented anywhere? I have the series of articles in Engineering in Miniature Vol4/5/6 which covered the 5"G version and these are useful but the 7 1/4"G drawings leave quite a lot to the imagination! (Not the least, what is the design WP of the boiler?)

Robin
Rugby MES
 

Replies To This Post

Xz

Joined: 1-01-92

Topics: 17

Replies: 244

Posted: Thu 3rd Nov 2011, 11:56am

Robin, the working pressure of a boiler is really down to the builder. Most work best in the 90-100lbs range, any less can leave you without sufficient puff in some situations and any more can be an embarassment when it comes to wheel slip getting away. I recall a gent some years ago who insisted on 125lbs for his Scot and discovered that it was almost undrivable from a start if blowing off, he soon dropped it to 100 and found it more than adequate. Of course, good firemen don't allow the boiler to blow off in the station anyway.
 

rmb5241

Joined: 1-01-70

Topics: 3

Replies: 4

Posted: Thu 3rd Nov 2011, 10:53pm

I wouldn't disagree with your comments looking at it from from a purely practical viewpoint. However, a boiler should be designed with safety in mind and therefore the designer should at least state the MAXIMUM working pressure he had in mind. That figure should should be used for the initial hydraulic test. Thereafter we use the boiler at whatever pressure we think is best provided we do not exceed that maximum design pressure.

So it would be nice if the figure was stated on the drawing?
 

Peter Beevers

Joined: 9-10-01

Topics: 3

Replies: 134

Posted: Fri 4th Nov 2011, 7:36am

I can only agree 100% with rmb5241 - calculations MUST have been done to prove the design safe, and these must have been done with a maximum pressure in mind. To exceed that is madness. And not to state it is similarly crazy. While the builder may choose to lower the pressure a boiler is used at, to raise over the design pressure is highly dangerous and invalidates all insurance.
Stating the design pressure of a pressure vessel is law.
 

Xz

Joined: 1-01-92

Topics: 17

Replies: 244

Posted: Sat 5th Nov 2011, 12:37pm

I totally agree that the info SHOULD be on the drawing, but often in the model world these things get forgotten. Yes we must comply with the regulations, but again, if working to the usual pressures of 80-100psi you should have no problem due to the usual over engineering in model designs. Often the exact gauges of material for these designs is no longer available and then we move onto the next thicker metric equivellent, giving even more leaway. Build to the published design, unless you want to exceed the usual parameters.
 
 
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