Double beat valve
Encyclopedia
Poppet valve
A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...
arranged to allow it to be opened against a high pressure with a minimum of force.
One of its uses is in steam engines to admit steam to the cylinders and to release the exhaust. In stationary steam engine
Stationary steam engine
Stationary steam engines are fixed steam engines used for pumping or driving mills and factories, and for power generation. They are distinct from locomotive engines used on railways, traction engines for heavy steam haulage on roads, steam cars , agricultural engines used for ploughing or...
s it is usually operated by trip valve gear while in railway locomotives a valve gear such as Caprotti
Caprotti valve gear
The Caprotti valve gear is a type of steam engine valve gear invented in the early 1920's by Italian architect and engineer Arturo Caprotti. It uses camshafts and poppet valves rather than the piston valves used in other valve gear...
is used.
It was invented around 1800 by Jonathan Hornblower
Jonathan Hornblower
Jonathan Hornblower was a British pioneer of steam power, the son of Jonathan Hornblower and brother of Jabez Carter Hornblower, two fellow pioneers....
.
His valve is in the form of a hollow cylinder provided with two seats of nearly equal diameter, at A and B in the diagram. The cylinder is connected to the actuating rod by a web. The force required to lift the valve depends on the difference between diameters D and d: the smaller this difference can be made, the less the force necessary to open the valve.
In Hornblower's valve, the steam flows past seat B only. In later developments of the valve, the central portion is waisted so that the flow can pass at A as well, so increasing the valve opening area for the same amount of lift.