On building Design #14 a Brotan Boiler

[cabbage]

Well today marks the end of the construction of my Brotan Boiler. Has it been hard -the answer has to no. But looking back on the construction -the order of assembly can only be described as critical!!!

What I got REALLY wrong was leaving the fixing of the "chin strap" piece at the base of the water wall until last. This left me with a vast amount of copper to get up to 650 deg C.

Order of assembly should be:

Fire tubes to front plate.
Super heater tubes to front plate. I did this the other way around and the devils own time getting the torch in.
Boiler wings to front plate of water wall. Try bending cold rather than annealing as it makes them too floppy.
Chin strap piece! Fit it now then you don't need the huge burner.

Fire tubes to rear plate of water wall.
Superheater tubes to rear plate of water wall.

Unify rear plate to boiler wings and chin strap piece
Assemble double domes and clench steam drier.

Insert clench and double domes to boiler barrel.
Insert top drum.
Connect cross drum.
Insert inner row of water tubes.
Insert outer row of water tubes.

Connect cross drum to water tubes.

Close off top drum and cross drum.


Problems:

The firebox (as such) is very wide and I am going to have to use two 28mm dia burners fitted with No.5 jets to provide flame across the water tubes. The boiler is probably more suited to a tank engine , because of the width, rather than a tender engine.

Would I build one again? The answer has to be yes. There is very little flanging and all the pieces are easy to construct. What I would do differently the next time is to increase the water tubes from 6mm to 8mm dia to increase circulation and decrease the thickness of the copper plate used from 2mm to 1.6mm. All the joints are external and if you have pinhole leaks they are easy to fill.

I now need to make the plugs to seal the holes and do the hydraulic shell test. Although I envisage it tootling around my tracks at 3BAR I will have it certified to 5.5BAR. The reason for this are twofold. The first is actually very simply to show that it is a solid workman like design. The second is that I have never found anyone who has built one of these -even though the design was published in the 1950's. This is the second boiler that I have built, and the first at G3 scale.

Tim has pointed out a "philosophical" problem with the water gauge, as the top and bottom of the water column  are not really obvious as to where they should be! After some head scratching I have decided that the top of the water lever will be the top of the boiler barrel -thus leaving the twin domes and clench drier in a steam area. The bottom of the water column will be to bottom of the top drum where it meets the rear of the water wall. This will give roughly 30mm of depth.

Now that I am leak free the next part of the project is to build the hydraulic testing equipment... Roy will send me the "Green Book" and the Certs. Once I have completed construction of it, I then have to persuade A.N.Other boiler tester to come to Derby and Certify my Brotan. I do plan to become a G3 boiler tester and doing Certs on my own boilers -is definitely NOT KOSHER!!!!

regards

ralph

[cabbage]

Having made the plugs to fill my bushes I am now left with the problem of constructing the fire box. This I intend to make out of 1mm thick 304 S/S. I have a "fabricator" (bend roll and guillotine) and I propose to make it double skinned with a layer of crushed vermiculite between them. The sections I will "pop" rivet together using A2 S/S rivets. The gaps between the water wall and the firebox I will seal with fireclay and the same with the burner plate.

The burners will sit on their brass plate held into position via a pair of capacitor clamps. I will probably have to section part of the main frames to get both gas nozzles to point in the correct direction. I have never tried the gas system "in anger" as yet.... The prior system of tests had to be abandoned because of the connecting plastic pipe melting. But this week I will "rough out" the copper pipe work and terrify the local populace again!!!

regards

ralph

[cabbage]

Today I proved the beast! I test fired the improved burner plate, the burners are offset and angled so the intercept all of the water tubes. The raw flames are circa 15cm long and have LOTS of little nice blue cones at the base...

The next test was out doors with the boiler perched with combustable support. The Work Mate has had it(!) So, with no holes plugged we lit the kettle and did an experimental boil.

The experimental conditions were far from ideal with breeze, no "firebox" or shielding at all. Nonetheless the boiler raised 700ml of water from 25C to 100C in 310 seconds. This means that the water tubes alone were absorbing circa 1kW from the burner plate. The waste hot gasses simply vented to the air rather than passing through the fire tubes -so this may be taken as a worse case test.

What I now need is some form of flexible gas piping that is heat proof to unify the burner plate to the tender gas tank -any ideas of a source?

regards

ralph

[John Candy]

Would neoprene be sufficiently heat resistant or would the metal attachment become too hot (I believe neoprene will withstand c.500F)?
Various diameters/wall thicknesses available at http://www.glrkennions.co.uk/sundries.html
Regards,
John.

[Peaky 556]

Ralph, I don't have a source, but as you may already know the best two of the reasonably common elastomers would be fluorocarbon or fluorosilicon. These are both superb with up to 450F capability, high abrasion resistance and unaffected by aliphatic hydrocarbons. On the other hand cheap and cheerful silicon rubber will cope with the high temp, but is poor on the abrasion and chemical resistance fronts. It would be worth a try in my view, but inspect it carefully for cracking after every use.
Tim

[Peaky 556]

Would neoprene be sufficiently heat resistant or would the metal attachment become too hot (I believe neoprene will withstand c.500F?

John, Neoprene is not one of the best for high temperature resistance; it's capability is more like 200 - 250F.

[Peaky 556]

Ralph
EPDM is widely available on eBay and better for temperature resistance than Neoprene. Chemical resistance is poor like silicone though, so be careful!

[cabbage]

Tim,

As I was in the area I went to Little Eaton. They have just the thing -maybe a little overkill but that is me all over!!! I bought three 1m lengths Red, Yellow and Blue. This will give me Gas and two Water lines.

regards

ralph

[cabbage]

Having been busy in the garden and taking advantage of the weather.... I now have to return to boiler work. I have built the "bolt on" fire box but before I unify the fire box to the boiler I have to pressure test the beast! I have TWO safety valves -one rated at 4BAR (abs) and another rated at 6.5BAR (abs). Everyones has advised me to have it certified at 6.5BAR (abs) or 80PSI above atmospheric. So, this is what I am going to do.

I have a pump and a pressure meter -it is rated at 1.6% FSD and a maximum operating pressure of 22BAR (abs) or 300PSI above atmospheric. It is filled with Glycerine too!

I am going to need to make a few DIY adaptors for it as my boiler does not have a 1/4BSP take off...

regards

ralph

[MikeWilliams]

A picture tells a thousand words Ralph ....

Mike

[cabbage]

This is true Mike.

Although I often get the feeling that the people looking at the pictures must think that the thousand words come from the Necronomicom...

I am in the process of getting some web space and horrifying the netizens!!!

Regards

Ralph