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Northumbrian boiler mistake ?

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John Willman06/06/2010 21:33:29
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On page 497 the rear view of the boiler gives a dimension of 2.625" to the top of the firebox, but this should be to the cenreline and the firebox probably 3.5".Sorry I forgot  to mention that this is the Northumbrian boiler.

Edited By John Willman on 06/06/2010 21:46:06

bellerophon09/06/2010 19:52:23
24 forum posts
I've found that the safety valve bush drawing also appears to be wrong - I bought one from GLR (no complaints about them they have been v helpful) and only when I machined the Bush B on the drawings in volume 204 #4376 I found that the safety valve is in fact 5/16" ME thread NOT 3/8 as shown on the plan!!!
 
I'm going to have to buy the full plan after all
 
Donald Campbell 

Edited By bellerophon on 09/06/2010 19:52:52

JasonB09/06/2010 20:17:26
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Interesting that as GLR list the safety valve as 3/8" x 32?
 
bellerophon09/06/2010 21:36:51
24 forum posts
I know - I've emailed them about it and will post their reply!!

Edited By bellerophon on 09/06/2010 21:37:53

bellerophon11/06/2010 16:12:49
24 forum posts
SAFETY VALVE
 
the safety valve opening pressure  is OK I spoke to GLR this pm they apparently got a batch threaded  5/16 ME from their supplier when they'd asked for 3/8ME but the pressure is the same so it just means threading the bush to 5/16 ME instead of 3/8
 
Also the only dome casting they have is for Rainhill - don't know if it's dimensions will suit Northumbrian yet 
 
 
 
Donald Campbell 
JasonB11/06/2010 17:14:35
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You also need to consider the size of the hole in the safety valve, it may well open at the same pressure but it needs to vent sufficient steam otherwise the boiler pressure may continue to rise.
 
Jason
bellerophon11/06/2010 17:34:33
24 forum posts
I spoke to GLR this afternoon and they assured me the valve was made to the correct specs except for the thread ie flow capacity and pressure settings
 
 
Donald Campbell 
bellerophon20/06/2010 20:49:19
24 forum posts
Anyone have a source for 20 SWG stainless tube?
 
Donald campbell 
JasonB21/06/2010 07:33:33
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Jason
Doubletop21/06/2011 11:42:06
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Posted by John Willman on 06/06/2010 21:33:29:
On page 497 the rear view of the boiler gives a dimension of 2.625" to the top of the firebox, but this should be to the cenreline and the firebox probably 3.5".Sorry I forgot to mention that this is the Northumbrian boiler.

Edited By John Willman on 06/06/2010 21:46:06

I've just found this. Can somebody please confirm John is correct and these plates should be 3.5" and not 2.625"
 
Pete
Doubletop21/06/2011 12:05:28
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I've just checked and 2.625 is certainly the dimension to the center line but I can't determine what height the firebox should be above the center line. It can't be 9/16" as it would then be in the way of the blower tube. Which means Johns suggestion of 3.5" would be incorrect
 
Drawings 71 (p 497) and 79 (p498) in part 11 of the series are certainly deficient in a number of places
 
Pete
 
(Two new firebox plates to be started tomorrow and now seeing why this project has apparently been abandoned by some)
Weary22/06/2011 09:49:48
421 forum posts
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Dimensions of the original LBSC boiler drawing for Rainhill:
Model Engineer Vol 84, No. 2085, April 24 1941, pages 328/9
 
Height of top of firebox from bottom of firebox: 3 3/4" (three and three-quarter inches).
Firebox bottom 1/4" (one quarter inch) lower than outer boiler plates.
Backplate height from bottom of lower edge of backplate to top of boiler 4 3/4" (four and three-quarter inches). Thus 5" (five inches) from bottom of firebox to top of boiler.
 
Blower stay 11/16" (eleven sixteenths inch) from centre-line of boiler and 1" (one inch) down from highest point of boiler. 'Balancing' 5/32" (five thirty-seconds of an inch) solid stay on other side of boiler.
 
Width over boiler plates at base of firebox 2 7/8" (two and seven-eights inch)
Width over firebox inner plates at base 2 3/8" (two and three-eights inches)
Foundation ring 3/16" (three sixteenths inch) square copper.
Width over firebox plates at widest point 2 1/2" (two and a half inches).
Firebox bulges outwards slightly at top to follow curve of boiler.)
 
Front to back length over boiler plates at firebox 3" (three inches)
Front to back length over firebox inner plates 2 9/16" (two and nine-sixteenths inches)
 
Tube number and layout, two 5/8" (five eigths inch) 20 gauge, nine 3/8" (three eigths inch) 22 or 24 gauge.
 
Hope that I have transcribed the dimensions OK.
Maybe some clues there as to missing dimensions?
 
 
Regards, Phil
 
 
Doubletop22/06/2011 10:59:38
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Phil
 
Thanks for the detailed reply. I don't have a copy of the Northumbrian articles to hand at the moment to check the original boiler against the recently published version. However, I believe they may be different. Tony Weir stated early in the series that he had made significant changes to the design, one being to lower the boiler as LBSC's version was too high. The tube layout you quote is certainly different. Tony's version, 10 x 3/8" 20swg tubes in three rows 7/16" between rows and 1/2" spacing in each row (off the top of my head as I drilled the tube plate today.)
 
I have worked out the length of the firebox plates to be 3.3125" allowing clearance for the blower, the thickness of the wrapper and a reasonable allowance between the top of the tubes and the plate flange. Hopefully that is 'right'
 
It has occurred to me, since posting the question and re-reading Martin Evans "model loco boilers" book that the firebox could extend below the foundation ring. Most of Martins designs did it that way and the dimensions you have provided for the LBSC version does the same. However, it could foul something in the frames, or not allow the grate/ashpan to fit. I have made mine a little longer as it can always be removed later without affecting the integrity of the boiler.
 
as an aside, on the subject of stuff under the firebox, how does that lubricator linkage work, surely it gets in the way? I'll save that for later though.
 
Thanks again
 
Pete

Edited By Doubletop on 22/06/2011 11:01:16

Tom Hart26/09/2011 15:18:15
2 forum posts
You might find the job a bit easier if you read carefully what Tony said about Rainhill in the first installment, and buy a set of his detailed full sized drawings.

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