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The pressure in the cylinder declines after cutoff as the steam pushes the piston down its bore. Cutoff is one of the four valve events. Early cutoff is used to increase the efficiency of the engine by allowing the steam to expand for the rest of the power stroke, yielding more of its energy and conserving steam. This is known as expansive working.
Used early on in electrical generation and to power ships, turbines were bladed wheels that created rotary motion when high pressure steam was passed through them. The efficiency of large steam turbines was considerably better than the best compound engines , while also being much simpler, more reliable, smaller and lighter all at the same time.
The steam turbine is the most efficient steam engine and for this reason is universally used for electrical generation. Steam expansion in a turbine is nearly continuous, which makes a turbine comparable to a very large number of expansion stages. Steam power stations operating at the critical point have efficiencies in the low 40% range ...
The WHE-25 engine has a 34% cutoff. [4] This allows for the remaining 66% of the piston stroke to expand the steam, extracting work from it and causing the pressure to drop. The figure to the right shows how pressure in the cylinder of a steam engine drops after the cutoff point. The WHE-DR must have a much later cutoff to allow it to self-start.
Cross compound engine, with an expansion valve (top) on the high-pressure cylinder. An expansion valve is a device in steam engine valve gear that improves engine efficiency. It operates by closing off the supply of steam early, before the piston has travelled through its full stroke. This cut-off allows the steam to then expand within the ...
The Ragonnet power reverse, patented in 1909, was a true feedback controlled servomechanism. The power reverse amplified small motions of the reversing lever made in the locomotive cab with modest force into much larger and more forceful motions of the reach rod that controlled the engine cutoff and direction. [4]
A Corliss steam engine (or Corliss engine) is a steam engine, fitted with rotary valves and with variable valve timing patented in 1849, invented by and named after the US engineer George Henry Corliss of Providence, Rhode Island. Corliss assumed the original invention from Frederick Ellsworth Sickels (1819- 1895), who held the patent (1829) in ...
An engine operating with no cut-off but a throttled steam supply will be operating inefficiently, owing to reduced expansive working and the risk of wire-drawing. The first 'automatic' governors were termed that because they not only controlled the speed, but could also take over the role of the driver and could vary cut-off too. [8] [9]