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Post by ChrisCrosskey on May 17, 2006 13:29:33 GMT
This is a question that probably will never be answered.....
What are the pro's adn cons of a Briggs boiler vs a wet firebox?... Are there any beyond simplicity of build on the one side and heater area on the other. ... I'm trying to imagineer a small loco, 5" narrow gauge, but sort of loosely based on an Italian prototype (std gauge but the inspiration rather than the rivet-counting copy) .... What I want to do is make it all myself, though I might be tempted to buy wheels..... BTW, it's that turbine engined thing that was in ME a month or so ago, I'd like to build soemthing like that but with teslas instead of normal turbines..... With no reciprocating valve gear to build/setup and a bunch of coffee grinders to power it I'm trying to keep the design simple. Before anyone asks, yes, four small teslas will easily pull a train with a few people behind it, my main worry is that I won't be able to make enough steam to feed them. As it's a turbine thing I can't imagine any boilermaker is going to be willing to go out on a limb and say that any standard boiler will do the job I want, so I'll build it myself. To keep cost and complexity down I thought I'd go for a Briggs, to allow it to be big enough to evaporate enough water I thought I'd go narrow gauge.....
comments (other than "bonkers") please
Comments especially welcome from anyone who owns/has built/has driven anything Briggs powered especially ifg they have experience of a wet firebox in a similar situation....
Aslo if ther are any resources on Briggs boilers I'd like to know.... I know they're popular in Australia but that's about it....
chrisc
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Post by steamjohn248 on May 17, 2006 21:59:17 GMT
Chris
Quite a large proportion of the heat given up by the fire is (I have always understood) absorbed by the water wall around the firebox front, back, top and sides.
In a Briggs boiler you only have front and top. Nuff sed, but they say they work, only one I've ever had dealings with was bloody awfull.
John
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Post by alanstepney on May 18, 2006 1:15:38 GMT
The very first Briggs boiler was built (by a Mr Briggs) for a 10_1/4" loco named Winnie, which is owned and regularly runs at Chichester ME club. Some years ago it needed a new boiler, and was re-boilered with a conventional boiler, which says something about the efficiency of both types.
I used to drive it, but dont recall if that was with the old boiler or the new. In any case, at that time it was only a short up-and-down track to wouldnt have been demanding for any type of boiler.
Before becoming Chichester clubs engine, it ran on Bognor Regis seafront for a while, then in Mr Briggs (senior's) garden for many years.
As an aside, Mr Briggs was an architect who made his money by patenting the "crash bar" used on emergency exits from public buildings: the one where one can lean against it and the door opens.
As for Tesla turbines, do you think you will need four? You may well find two sufficient.
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Lee
Involved Member
Posts: 95
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Post by Lee on May 18, 2006 7:08:59 GMT
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Post by ChrisCrosskey on May 18, 2006 9:18:37 GMT
Ah.... already I see one common misconception coming to light... Briggs boilers do have waterwalls, not just the firebox crown and tubeplate, however the walls are made from copper tubes in an old-fasioned radiator styleand effectively act as a thermosyphon between their lower feed (from the bottom of the tube-plate) to their upper exit (onto the firebox crown)..... It doesn't quite give you the heating area of a full wet firebox but it isn't that far short.... and it's a heck of a lot simpler to make than a fully stayed boiler
As I'm not trying to do an exact model of anything I can always make the firebox a bit bigger anyway..... as a thought some calculations of the back of an envelope kind...
Plan on using a wheel with an approx 3 1/2 inch rolling diameter the turbines will be directly geared onto an internal ring gear of approx 3 inch (75mm or thereabouts) diameter on the outboard side... the turbines themselves will have a gear of approx 3/8" (10mm) machined into the end of the shaft.... If I use half-mod gears then that works out at 18:149 gearing (I want to even out the wear so lets go to 75.5mm on the ring gear), that's a gearing of 1:8.28.... Now from another quick calculation a wheel give 1 mile per hour per inch of diameter per 336 rpm, so a three inch wheel at 336 rpm gives 3mph, lets set an upper speed limit of 9mph flat out and we're looking for 1000rpm at the wheels, giving us a turbine speed of 8280 rpm, which means I can reasonably run its bearings as pre-sealed greased balls and not need anything more fancy. If I use 2mm stainless for the turbine blades and a 1mm gap then I get 15 blades into a bit less than 2", and I would expect the whole turbine assembly to be a bit less than 3 1/2" wide, giving an overall width to the engine across a wheel/turbine setup of about 12" (5" across the wheels with the turbines mounted outboard of them)... I'm guessing here but a 3" diameter turbine should be adequate, adn I think you're right, I could probably get away with just two.... if it doesn't work properly then I can always nick the boiler off it for something else and barring the wheels the rest of it comes out of my pile of assorted metal anyway......
I've been reading the boiler code and as far as I can tell if I make the boiler myself and don't plan on selling it commercially I don't need to have all the traceability documents for the tubing, which menas I could just get a piece of thick-wall copper tube from College Engineering or similar along with the appropriate bits of plate and smaller pipe and silver solder it together .... is this other peoples opinion too? The boiler, the ring gears and the wheels are the only bits I'll really need to buy, adn only the wheels will not be useable for soemthing else.....
chrisc
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Post by chris vine on May 18, 2006 22:29:36 GMT
Hi Chris,
It seems to me that the most unpredictable part of your whole proposed (fantastic!) machine is the turbines.
Maybe you should make one turbine first, run it from a boiler with sufficient capacity and test its power output, torque and speed at which it seems to run well.
After that you will have a better idea of the boiler size needed and can make that.
If you then have a working "guts" of a locomotive you can then make the rest, having some certainty that it will work.....!!??
Chris.
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Post by greasemonkey on May 19, 2006 7:28:35 GMT
Hi Chris C
I would have thought your first problem would be getting your new boiler design approved under the pressure vessel regulations. Maybe others could comment on this area?
Andy
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Post by ChrisCrosskey on May 19, 2006 8:55:00 GMT
IS this really likely to be a problem?... I was going to try and find an already approved design if possible, though if i don't then I will overengineer, 1/4" wall thickness and similar plate for the crown and tubeplates for instance.... I guess I'm looking for about 120psi .... Who would need to approve it, the boiler inspector or some quango in London?.... Also on a Briggs the waterwalls are a seperate piping structure at the firebox end of the boiler, are they part of the test for the boiler regs or no (like superheaters)... I'm assuming they are as they are not "downstream" of a valve but are permanently attached and effectively always on.....
chrisc
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