Romulus Lesley's Boiler Clean-out & Foundation Ring Repair ....*
* Modifications for "over the fire" air inlets are shown further down the page. Click on the thumbnails for images at 800 x 600 pixels.
Before starting any repairs or modifications such as are described here yourself, make sure that the work is approvable by your club boiler inspector and within the applicable rules of your local boiler authority.
A routine winter inspection and clean-out turned into a bit of a project when pulling the inspection plugs revealed that the firebox water legs needed more than just a poke with a rod and a quick rinse, they were completely plugged! Twenty years of hard use by more than one owner had left their mark.
Once the boiler was off and uncovered, three holes were drilled up through the foundation ring to reveal a solid deposit. No amount of digging and poking made much difference, neither did a weak muriatic acid wash, little of anything ran out of the blowdown connection, nothing at all from the washout plug holes.
Cutting off the foundation ring is a rather drastic way to access the water spaces but seemed to be the only way to get all the crud out. An hour with a small hammer and an old screwdriver blade served to remove most of the blockage. After the rust, scale and mud dried out it weighed four pounds, all taken from the half-inch wide water legs around the 7" x 7" inner firebox. All four sides were solid for a distance of two inches up from the ring.
A view up a water leg showing welded-in rod stays and more than a little surface corrosion on the plates. Right photo: a look forward inside the barrel through a backhead bushing hole. Clean copper tubes and corroded longitudinal stays are visible below the throttle rod.
A trial fit of a piece of the new "U" shaped foundation ring (left) and "all ready to weld" (right). This boiler was built with girder crown stays so the question of how to support the inner firebox arose. The AMBSC boiler code (my preferred reference work) disallows girder stays when there is a foundation ring of any type. My solution (for use in Ontario, Canada) was to beef up the rod stays so that the crown sheet load, about 5 tons under hydro test, is taken between the heavy firehole ring and the new heavier throat sheet stays. The "U" ring is considered not to be supporting any download although it does contribute to that. Six additional new stays in the side sheets are providing strength above that actually required for safety. My preferred method of supporting the firebox is to use stays from crownsheet to the outer shell, not girder stays but this was a repair not a complete re-build and there was no room to add crown stays.
Almost all done and ready to test. Eight new 3/8" npt washout plug bushings and a 1/2" npt blowdown valve connection are fitted. Right photo is a view down an inspection port looking into the new "U" shaped foundation ring.
An air test to 40 psi found three small areas of weld porosity that were ground out and re-welded. A "post repair" hydro test to 1.5 times the working pressure of 100psi was then successfully performed. Heath Robinson would have been proud of this lash-up of pipes and hose!
.... and Some Modifications
Part of the re-staying involved adding support for a brick arch and some "over fire" air inlet vents as described by L. D. Porta for his locomotive gas producer combustion system (GPCS). While I don't intend to fit full GPCS to Lesley, our local club coal is high in volatile matter and smoky, additional top air seems like a good idea.
The total air inlet area to grate area ratio is that used by David Wardale for his SAR 19D locomotive. Whether this is right for Romulus I can't say until test runs begin but it is a place to start. (It seems right see photos below.)
Three new 3/4" diameter rod stays are fitted to the throat plate. The top one has a 3/8" dia. air inlet hole and is extended a little on the inside to form part of the brick-arch support. The firebox sides get one more each of these air inlet/arch support stays plus one solid stay and a second air inlet stay. The ratio of top air to grate area is .021:1.
The red arrows point to two air inlets in the side plates. The green arrow points to a half-round duct to bring pre-heated air up the firebox side. The finished duct installation will also prevent the insulation, cladding and side tanks from blocking the vents.
Two views showing the brick "arch" made from a flat 1/2" thick BBQ brick, supported on three of the extended air vent stays. The left view also shows the grate support bars tacked to the foundation ring. These bars are a little thicker than strictly necessary in order to make the boiler sit level after the loss of material from cutting off the old foundation ring. The ends of the four air ducts are also just visible. The brick is a "Grillpro Flarebuster" gas grille firebrick. 3-1/2"x7-1/2"x1/2" as supplied in a box of nine.
A quick coat of aluminum paint and we are ready to re-fit the insulation and cladding.
Now that is a working blowdown! There is one on the other side too.
Do over the fire air ports work? Before (L) and after (R) photos prove that they do. The coal was from the same load each time.
Caution
Before starting any repairs or modifications such as are described here yourself, make sure that the work is approvable by your boiler inspector and within the applicable rules of your local boiler regulations.
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