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Post by eightpot on Aug 31, 2015 22:42:02 GMT
I need to do some modifications to a boiler design, one being to substitute 7/16" x 20 gauge tubes for the 1/2" x 20 g specified. However, for the tube length 0f 13-3/4" are the 7/16" ones considered too small for the lent, or would the 1/2" be preferable? This for a narrow firebox boiler fitting between the frames. Thoughts, anyone?
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Aug 31, 2015 22:58:12 GMT
i would use 1/2" dia tubes for that length, but 7/16" OD will be ok and within the Keiller formula. if the 7/16" OD tubes also allow a better tube stack arrangement with more tubes then you will be quids in so to speak as having a freer gas flow. if however the number of 7/16" OD tubes remain the same as the 1/2" OD tubes then you are reducing the free gas flow and will result in a not so free steaming boiler.
what loco and design are you working to?
cheers,
julian
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Post by eightpot on Sept 1, 2015 23:00:08 GMT
It is Martin Evans LNER 2-6-2 tank loco 'Enterprise' in 5" gauge. The problem is that it is a 5-1/4" inside diameter barrel and round top outer firebox wrapper.The inner firebox has only 1-7/8" between the top of the firebox crown and the outer wrapper which in my view is insufficient room for keeping a safe water level. I'd like to lower the firebox to increase this distance to (say) 2-1/4" but this looks like overcrowding if the existing design 1/2" tubes are used. Haven't tried it on paper as yet, but wondering if 7/16" tubes offer a solution.
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Sept 1, 2015 23:50:50 GMT
hi eightpot,
there isnt anything wrong with the boiler for martin evan's 'Enterprise' and it is one of his better designs. there is nothing wrong with the height of the firebox crown.
Geoff (Routledeg on the forum) has an excellent example and if Geoff reads this i am sure he will reassure you as to boiler being ok.
many of martin evans' boiler designs are criticized as having too low a firebox crown, but Enterprise isnt one of these.
cheers,
julian
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Post by runner42 on Sept 2, 2015 1:47:05 GMT
Martin Evans in his book on boiler design and making suggested that the firebox crown should not be more than a certain fraction of the barrel diameter above the barrel centre line. Unfortunately this fraction I don't remember, but if someone can provide this it will be an interesting exercise to see if his Enterprise design meets this criterion.
Brian |
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