VFT insulation

[Lopez Mike]

From what I can find here on the forum and with some web searching, there seems to be a fairly wide range of schemes for VFT insulation. Most seem to be using wood lagging but with and without anything under it.

My present boiler had a thick (over 1") glass wool blanket with 3/4" of wood over it. The blanket was crudely encased in glass cloth using what apeared to be a mixture of flour and water. The second that moisture hit there was a sticky white goo everywhere. That stuff is all in the garbage can now!

I'm looking for advice about good ways to keep stray moisture out of the blanket and still be able to remove it later without destroying it. Maybe heavy aluminum foil?

I'd like to hear people's experiences and opinions on this.

[gondolier88]

You can buy proprietry foil wrapped cermaic wool insulation from Heritage Steam Supplies here in the UK- I imagine it is also available in the US. It isn't too cheap, but it works a treat.

Greg

[fredrosse]

Rather than a foil, you could use ordinary aluminum flashing, pop riveted together, or screwed with sheet metal screws. That is what encases the fiberglass insulation around the Margaret S. boiler, and working with it is easy, rigid enough to hold a shape, and can be cut with ordinary scissors. Wood over that would work. If you need to waterproof seams, the silicone caulks are often rated for high temperature, up to about 500F.

I used ordinary house fiberglass insulation left over from an addition project. The bats were 15 inches wide x 6 inches thick, but could be parted to about 1-1/2 inch thickness without much trouble. I just removed all the lagging and insulation for my burner change-out, and I will be able to re-use almost all of the insulation, although it is very cheap anyway.

Ceramic insulation, or mineral wool, is needed for high (firebox) temperatures.

Ordinary fiberglass and wood can take the temperatures of our pressure vessels, such as the outer shell of a VFT. 150 PSIG (about 10 Barg) corresponds to 366F (185C). About 1 inch of fiberglass insulation knocks down the wood lagging temperature significantly. With 1 inch fiberglass under 3/4 oak lagging, the wood is all under 200F, and the surface of the wood is about 110F - 120F in calm air surroundings.

[Lopez Mike]

Greg,
I'll check out the ceramic stuff though I already have my glass blanket.

Fred,
Good idea about the aluminum flashing. I'm used to working with the stuff as I built an airplane out of aluminum once. With some hi temp RTV to seal up a few critical places I think I can do a decent job. My boiler has a water leg so the only place that gets any hotter than the steam is just around the firebox door. I'll leave a small air gap there anyway.

Now to go re-saw the mahogany and set up my planer and jointer to the right angles and stuff. The top closure on the wood is going to be a fiddle at best. It amounts to a ring about 17" ID by 23 inch OD and 3/4" thick made out of several curved pieces of the mahogany. Oh well. The cat is used to bad language by now.

[Mike Rometer]

Mike, a tip about ceramic fibre. Pottery kiln makers use reams of the stuff. If you can find one near enough to you, try begging/bidding for the offcuts, they can be quite sizeable and that stuff is really good. It comes in many thicknesses, I have some 2" put by.

[Lopez Mike]

Mike

After reading your post I went and looked at my insulation blanket and I think it might be ceramic fiber. I'll go out later and hit a bit of it with a flame and see if I can get it to melt. Glass melts under even a propane torch. This stuff should survive warhead re-entry into the atmosphere!

I didn't know such a thing existed. Wild overkill for my boiler that doesn't get above 360F. But good insulating properties though.

Thanks

[Lopez Mike]

Checked it out. It's fiberglass. Fine for what I'm doing though.