Boiler Design

Theres a fully automated XL spreadsheet which will work it all out for you, both copper and steel. Calcs yube thickness, stay pitch etc. I remember for steel it uses a safety factor of x4. My inspecter cross referanced his calcs against the program and had no issues with it.

hi phil

i knew don young and he used to supply all the relevant calculations with his boiler drawings for ME. these were checked (he presumed!). the only comment i recall is don being told his safety factor was too great and his plate thicknesses over generous and his stay pitch could be more. he refused to alter his designs which although entailing more work would have reduced the safety factor. i only recall martin evans providing his own calculations for his own boilers and putting them in print when he was heavily criticised over a design. generally the 'calculations' arent published by ME.

what may be a perfectly adequate joint for a professional experienced boiler maker can be a can of worms for a beginner, hence what is often a belt and braces approach with regard to flanges etc.

there are some classic 'bad designs' some old (eg LBSC's BRITTANIA throatplate) and unfortunately some new. a bit of thought and common sense and advice from your boiler inspector will avoid the pitfalls of design AND construction. (a well designed boiler badly made with porous joints or inadequate penetration of the silver solder is as dangerous as a bad design). some of martin evan's 'novel' ideas at simplyfying boiler construction in the 1960's are regarded as pretty 'iffy' these days.

catastrophic failure causing injury (according to the late Jim Ewins) is most likely to occur with a barrel seam coming apart or a dome blowing off when fixed with steel as opposed to stainless or hard PB bolts. unfortunately i still see lots of ordinary steel bolts fixing domes.

i cant imagine you will have a problem reducing your barrel diameter and altering the location of some bushes. however i personally wouldnt reduce the boiler diameter for the sake of saving £35-45 in buying a new piece of tube. it will muck up the tube spacing and water circulation of the boiler and could mean the difference between an excellent steaming boiler and something quite mediocre. although the barrel doesnt contribute much to heat transfer via the tubes to the water, the effect on water circulation would possibly be detrimental, and any alteration required by the smaller barrel in the number of tubes will have an effect on the free gas flow through the boiler which IS very important IMHO. so unless you know what you are doing and can predict the effect of any changes on boiler efficiency too i would stick with the boiler as designed. after all, you will be using considerably more silver solder in value than the cost of a new bit of barrel tube.

i am not familiar with the NORTHUMBIAN boiler design.

cheers,

julian