Superheater Elements

[martyn1936]

I am building Paddington a 7 1/4" 15xx and have come to the point of fitting the superheaters. I have bought 4 Polly Elements, the type where the two pipes are bent over and welded at the spear and my question is where do they finish in the firebox? Do they go back and almost touch the rear of the firebox , do they just poke out of the end of the tubeplate or somewhere in between?
Martyn

[millman]

If they are stainless elements they usually go to the rear of the firebox.

[uuu]

Yes - they pick up a lot more energy from radiation within the firebox than absorbing it from the flue gases in the tubes. So for maximum effect, have them go almost to the back.

That will have some consequences: with higher temperature steam, the o-rings and other degradable components downwind of the flow will need to be rated accordingly. You'd also need to ensure your lubrication is OK - not that you need to use the almost-solid gloop, just be aware.

And shortening them later is easier than stretching them! Not that you'll need to.

Wilf

[JonL]

Agree, almost touching the rear of the firebox. The more that can be hit with the radiant heat from the fire the better.