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Previous Featured Engineering Project:

Boiler water-level gauge glass valves:

This month we are producing a pair of sight glass valves that fit onto the rear of a locomotive boiler, they allow the engine driver and fireman to view the water level. The valves feature two internal safety anti-blow-by valves that will stop the sudden escape of steam in the event of a glass failure - and also a small drain cock that allows the ability to flush out the whole unit to clear the sight glass of any dirt or residue that may be stuck to the inside of the glass tubes.

Setting of the castings into the four jaw chuck is all important. As we are machining the component from every face, most of which need to be parallel or at right angles to each other - we must take great care on the first few faces to ensure that the castings are set correctly. I first machine the flange face that mates to the boiler to provide a 'datum', then machine every face of the casting using this machined datum as a dimensional reference to ensure that everything remains square and correctly orientated. As the casting is not perfectly square i am careful to 'clock' both the front and back faces so that I can set the part to maintain an

average 'run out'. This ensures that once the casting is reversed in the chuck that there will be enough removable material to give a good clean machined face on all sides of the part. Where possible I always machine the components in one setting, so that in some cases the lathe tools must be used upside down and turned in reverse in order to easily ensure that all machined parts remain perfectly true. (this is handy to speedily machine a component with only LH ground tools). As we manipulate the castings in the chuck I use a accurately machined 'clocking bar' that I have previously machined to neatly fit into the bore of each port of the part.

Care must be taken at times because the weight of the component is offset, so either a counter weight is used and attached to the rear of the chuck, or we machine at a reduced speed. All of the components are finely finished, a sine bar is used to set the compound slide to produce the internal tapers and valve seats to ensure that all of the parts are completely steam tight once assembled. We machine a hardened square broach to profile the handle square drive, in this way we can obtain a good tight fit onto the stainless steel valve stem.

The assembled parts are tested by pumping water into the inlet at high pressure to ensure that the castings are not porous and also that the valve mechanism remains water (steam) tight under abnormal operating conditions.

We are currently producing several of these units and are proud that these will be used on the locomotive 'tornado' to monitor the boiler water level. They are manufactured to the original part drawings and will certainly remain in use for many years to come.

Component was featured on the website home page (July 2012).


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