Tuesday, 13 January 2015

New Chimney Bases Fitted

Midsomer Norton Station's Aerial convergent plate-way has been resurrected to assist with moving the heavy new chimney base castings into place on top of the boiler.
Progress on top of the boiler
After a long spell outside, Sentinel 7109 has now found some shed time for restoration activities. A previous article set the scene.

However, the progress shown above misses the steps involved. It began with manhandling of the first casting from floor level to the top of the boiler where the aerial convergent plate-way could take over.
Looking towards the rear, the first casting is held by the strap
The trolley jack is ideal for this purpose as everything happens slowly and avoids damage through bumps and drops in the wrong place.
Casting moved above the final location
The jack can run along the 'rails' to move the casting in to place.
Not all is perfect
The new castings are much more solid than the old ones and thus the cut-out for the superheater retaining nut was not quite big enough. A small amount of the casting had to be ground away using an angle grinder to make it fit.
Extra cut-away to accommodate the nut
This was a dry run to check for fit. Then it was time to do the job properly.

When exhaust steam blasts up the chimneys, air should be drawn up through the firebox. If there is any leakage between the chimney and the boiler top plate, the suction will be reduced and steaming will not be as efficient as it should be.

I concluded that to merely bolt down each casting on to the top plate would not be good enough and that a gasket of some description would be required.

I was recommended to have a look at the Vitcas website for inspiration. I found some ceramic felt tape about 10mm wide and 3mm thick and some fire clay mastic.

I used the mastic to stick the tape in place as in the photo below.
Ceramic 'felt' seal around the chimney base
Then the casting could be lowered into place without risk of displacing the tape. It was feasible to put the tape right on the edge of the top plate's hole as the hole in the casting coincided well.
Casting fully seated (1)
Casting fully seated (2)
The tape protrudes slightly on the side nearer the centre line but this will not be a problem.

It's worth noting a previous article about the sinking centre section of the boiler top plate. Before putting the castings in place, I slackened the nuts which hold the strut supporting the superheater's baffle plate. This left the top plate so that it would be flattened when the castings were tightened down and indeed this was the case. The baffle plate can then be tightened up.

The second casting was handled in the same way as the first and went in without needing to grind away space for the other superheater nut.
Both castings in place
RHS Bifurcating exhaust pipe fitted
View down through to the superheater showing the blast nozzles
(My boots were clean at the start of the day!)
The bifurcating exhaust pipe to the right is still to be fitted. Then there are the four tubes and outer heat shields to fit. A new cover will be needed to keep the rain out as the chimneys will protrude out through the cab roof.

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