The Steamboating Forum

Good morning.
What’s the best method of insulating the firebox on a Lune Valley boiler?
At present mine has only the sides fitted.
TIA
Ian

If the flame never contacts the walls, a thin high temp. stainless (US alloy designation 310) sheet backed w/ Fiberfrax or similar insulation works well. If the burner washes the walls with flame, you'll want a castable refractory, I think, in order to last.

- Bart

Hi Ian, on my lune valley boiler (solid fuel) I made the casing out of 25mm square tubing. I could then use a ceramic fibre insulation about the same thick ness . I clad the out side in stainless steel about 1mm thick, on the inside of the fibre insulation I used a stainless steel mesh to hold the fibre in place.
I had a old kilm and used the soild bricks out of that around the grate so the 'coals' do not touch the ceramic fibre. I also used these alongside the bottom drum . High for the solid bricks is just over want I thought the fire might be and are about 4- 5 inches high. On the back wall I used taller slabs of these fire bricks about 8 inchs high . I also stuffed ceramic fibre around the outside of the two drums . It has done a seasons firing as is all OK.
The out side temperature of the boiler varies , just warm to the touch on the 2 drum side to just a bit to hot to hold your hand agaist it on the other but still no where hot engouh to burn.

Mike

Mike Cole wrote:Hi Ian, on my lune valley boiler (solid fuel) I made the casing out of 25mm square tubing. I could then use a ceramic fibre insulation about the same thick ness . I clad the out side in stainless steel about 1mm thick, on the inside of the fibre insulation I used a stainless steel mesh to hold the fibre in place.
I had a old kilm and used the soild bricks out of that around the grate so the 'coals' do not touch the ceramic fibre. I also used these alongside the bottom drum . High for the solid bricks is just over want I thought the fire might be and are about 4- 5 inches high. On the back wall I used taller slabs of these fire bricks about 8 inchs high . I also stuffed ceramic fibre around the outside of the two drums . It has done a seasons firing as is all OK.
The out side temperature of the boiler varies , just warm to the touch on the 2 drum side to just a bit to hot to hold your hand agaist it on the other but still no where hot engouh to burn.

Mike

Brilliant, just what I needed to know.
Thanks
Ian

Mike Cole wrote:Hi Ian, on my lune valley boiler (solid fuel) I made the casing out of 25mm square tubing. I could then use a ceramic fibre insulation about the same thick ness . I clad the out side in stainless steel about 1mm thick, on the inside of the fibre insulation I used a stainless steel mesh to hold the fibre in place.
I had a old kilm and used the soild bricks out of that around the grate so the 'coals' do not touch the ceramic fibre. I also used these alongside the bottom drum . High for the solid bricks is just over want I thought the fire might be and are about 4- 5 inches high. On the back wall I used taller slabs of these fire bricks about 8 inchs high . I also stuffed ceramic fibre around the outside of the two drums . It has done a seasons firing as is all OK.
The out side temperature of the boiler varies , just warm to the touch on the 2 drum side to just a bit to hot to hold your hand agaist it on the other but still no where hot engouh to burn.

Mike

What’s the reason for stuffing the ceramic fibre around the outside of the two drums?

Thanks
Ian

Ceramic fiber insulation works very well, but cannot handle either direct oil flame impingement or regular casual contact with solid fuels such as coal or wood. Thus, the firebox itself needs an inner liner that can both deal with the temperatures and the contact. This liner material can be a relatively poor insulator; it's principle job is to protect the ceramic fiber. I've used insulating firebrick, stainless steel and castable refractory for this task in an oil fired boiler; the relatively weak firebrick could not handle the shock loads from getting trailered several thousand miles, and the stainless steel lasted 15 years but should have been replaced earlier. The castable refractory has proven quite sturdy and shock resistant although somewhat heavy.

Such construction is common in home built oil fired foundry furnaces.

- Bart

ianrichards wrote:

Mike Cole wrote:Mike

What’s the reason for stuffing the ceramic fibre around the outside of the two drums?

Thanks
Ian

only on the outside side of the drum not the fire side

mike