You must warm up a steam engine when you open the throttle. The cold cylinders make steam condense, and then you have water, which does not compress. You open the petcocks on the steam chest and the cylinders to allow that water an escape route, or the engine will lock up suddenly when the piston hits a wall of water. Warming up a traction engine is not as dramatic as a locomotive. There is less iron, and as you make the engine turn it is not moving all the mass of a loco. When you start a cold locomotive you must be extra careful, because if you hit that water with the weight of the engine, things are going to break. It makes for a great show. Thank You, Merle, for spotting this one!
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2 comments:
Do I understand this is on starting out with a cold engine? That the exhaust from each cylinder is directly vented so that any water that condenses in the cold cylinder is pumped overboard rather than causing hydraulic lock?
OK I can see that... It seems to me then the petcock is a short circuit to the normal steam exhaust path? Which I gather is out through the chimney with the firebox exhaust?
Yup! You got it! When the cylinder is warmed up the petcocks can be closed. The bigger the engine, the longer you let them blow, because you have more iron to warm up. You crank the mechanical oiler for each cylinder several turns before you start, because the steam blowing through will clean oil out of the cylinder.
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