The double-beat valve, drop valve or equilibrium valve is a type of

poppet valve A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapor flow into an engine. It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usual ...

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 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 ...

s it is usually operated by

trip valve gear Trip valve mechanisms are a class of steam engine valve gear developed to improve efficiency. The trip mechanism allows the inlet valve to be closed rapidly, giving a short, sharp cut-off. The valve itself can be a drop valve or a Corliss valve. T ...

while in railway locomotives a valve gear such as Caprotti is used.

Hornblower's valve

It was invented around 1800 by

Jonathan Hornblower Jonathan Hornblower (5 July 1753 – 23 February 1815) was an English pioneer of steam power. Personal life The son of Jonathan Hornblower the Elder and the brother of Jabez Carter Hornblower, two fellow pioneers, the young Hornblower was ...

. 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.

Cornish valve

In the early nineteenth century the double beat valve was known as the Cornish Valve, a synonym that persisted until the early 20th century. The Cornish valve gear, as used on early beam engines, was invented by Murdock, an assistant of

James Watt James Watt (; 30 January 1736 (19 January 1736 OS) – 25 August 1819) was a Scottish inventor, mechanical engineer, and chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1776, which was fun ...

, in 1820.

Valve gears

Double-beat poppet valves became widely used during the nineteenth century. Francis Stevens invented the Stevens valve gear, a double beat poppet valve, in 1839. It was used throughout the nineteenth century and in the early years of the 20th, on side-wheel paddle steamer engines, including the grasshopper engine, in the United States. The Lentz gear, of German origin, was first applied in Germany in 1899 where it became widespread, and was subsequently also manufactured in the United States. The Putnam engine, a high pressure variable cut-off steam engine built by Putnam Machinery Co. in the United States, featured four double beat poppet valves operated from a single camshaft.

References

{{steam engine configurations Engine valves

Hornblower's valve

Cornish valve

Valve gears

See also

References