Thursday, 8 December 2011

No. 1 Alan Bloom maintenance

Boiler separated from chassis
Every five or so years, Bressingham-built No. 1 Alan Bloom requires a bottom end refit, so this year's maintenance job is rather more substantial than usual — wheel re-profiling, valves and valve gear, slide bars, bushings, some shimming and whatever else turns up.

Part of the tender wagon, the hoses are for the compressed air braking system

Boiler from the firebox end

Wheel re-profiling

Over time, the wheels on any locomotive or carriage will wear down, even with the slow speeds on Bressingham's narrow gauge track. With the cost of a new two-foot axle set into four figures it makes sense to extend the life of existing wheels where possible.

This is achieved by building up the wheel flange using an arc-welder. As with everything, there is a process laid down to ensure that it is done properly using the correct technique and materials.

Once the wheel has been built up, it's then put onto a lathe, turned to achieve the correct profile, and given a new lease of life.

Hoisting an axle onto the lathe for re-profiling the wheels

These wheels have been re-profiled

Bottom end refit

The "bottom end"

New brass bushing
On a workbench, Tony is assembling the valve gear. All of the brass bushings have been removed and replaced with newly machined ones. Even though they are regularly oiled (during locomotive preparation and during the day) I'm amazed that they still last five or more years given the wear they get. The valve gear connects to the eccentrics (visible between the two wheels in the image of the axle being hoisted onto the lathe) at one end and the valve at the other.

Valve block with brass valve

Underside of the valve and the ports in the block

As the wheels rotate, the valve gear slides the valve back and forth over the cylinder block. Here pressurised steam is directed to the appropriate side of the piston, whilst the opposite side is exhausted — all depending on the position of the wheels and thus pistons as everything is interconnected — much like the job of a timing belt on a car engine. No electronics here, everything is totally mechanical.

Valve gear laid out

When everything has been refitted, Tony tells me that they will push the bottom end along and time it up. The difference between correct and incorrect timing can be as little as a half-turn on the threaded bar shown at the bottom of the image above!

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