How It Works: The Corliss Valve Gear Of Crossness Steam Engines

At south-east London's Crossness Pumping Station
( http://www.crossness.org.uk/ ) you can see four rotative beam engines. One of them -- Prince Consort -- restored to working condition, another one -- Victoria -- in restoration and the two others -- Albert Edward and Alexandra -- still in their abandoned state. These engines, originally single cylinder Watt engines, got an update in 1899 to three-cylinder compound engines (steam is used three times -- first in a high, then in an intermediate and at last in a low pressure cylinder). The original cylinder served from that time as low pressure cylinder, the two new cylinders, on the right side got a new Z-link parallel motion. See my other Crossness video    • The Biggest Operating Rotative Beam S...   . The engines were fitted with a Corliss valve gear, invented by the brilliant American engineer George Henry Corliss. See http://en.wikipedia.org/wiki/Corliss_...
This valve gear uses four rotary valves (working similar to a gas tap). These Valves are operated by camshaft driven rods. The camshaft itself is driven directly from the flywheel by the help of a bevel gear. The big advantage of this gear is, that the timing of the inlet valve can be changed via the governor. (All those features were invented a long time before modern car engines used variable valve timing). This allows a constant engine speed independent of work load and otherwise a saving of fuel. At small work load steam admission is cut off earlier and most of the work is done by steam expansion.The inlet valves are closed and damped by the help of dashpots, working similar to a car's air suspension with shock absorbing.
I have gratefully used the great public domain animation of Charles J. Dockstader http://www.billp.org/Dockstader/Valve... for a better explaining of the working principle.
Thanks for watching!