The slide valve is a rectilinear

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or Slurry, slurries) by opening, closing, or partially obstructing various passageways. Valves are technically Pip ...

used to control the admission of steam into and emission of exhaust from the cylinder of a

steam engine A steam engine is a heat engine that performs Work (physics), mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a Cylinder (locomotive), cyl ...

Steam engine slide-valve cylinder animation

Use

In the 19th century, most steam locomotives used slide valves to control the flow of steam into and out of the

cylinder A cylinder () has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infinite ...

s. In the 20th century, slide valves were gradually superseded by

piston valve A piston valve is a device used to control the motion of a fluid or gas along a tube or pipe by means of the linear motion of a piston within a chamber or cylinder. Examples of piston valves are: * The valves used in many brass instruments * ...

s, particularly in engines using superheated steam. There were two reasons for this: * With piston valves, the steam passages can be made shorter. This reduces resistance to the flow of steam and improves efficiency. * It is difficult to

lubricate Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubric ...

slide valves adequately in the presence of superheated steam.

Murdoch's D slide valve

The D slide valve, or more specifically Long D slide valve, is a form of slide valve, invented by

William Murdoch William Murdoch (sometimes spelled Murdock) (21 August 1754 – 15 November 1839) was a Scottish chemist, inventor, and mechanical engineer. Murdoch was employed by the firm of Boulton & Watt and worked for them in Cornwall, as a steam engin ...

and patented in 1799. It is named after the hollow central D-sectioned piston. This valve worked by "connecting the upper and lower valves so as to be worked by one rod or spindle, and in making the stem or tube which connects them hollow, so as to serve for an induction pipe to the upper end of the cylinder." This allowed two valves to do the work of four. The above description (referring to upper and lower valves) clearly relates to an engine with a vertical cylinder, such as a

beam engine A beam engine is a type of steam engine where a pivoted overhead Beam (structure), beam is used to apply the force from a vertical piston to a vertical connecting rod. This configuration, with the engine directly driving a pump, was first used b ...

. Where the cylinders are horizontal, as in a

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, Fuel oil, oil or, rarely, Wood fuel, wood) to heat ...

, the valves would be side-by-side.

Balanced slide valve

The balanced slide valve was invented by the

Scottish Scottish usually refers to something of, from, or related to Scotland, including: *Scottish Gaelic, a Celtic Goidelic language of the Indo-European language family native to Scotland *Scottish English *Scottish national identity, the Scottish ide ...

engineer Alexander Allan. It was not much used in the UK but, at one time, had great popularity in the United States. It gave some of the advantages of a piston valve to a slide valve by relieving the pressure on the back of the valve, thus reducing friction and wear.

External links

The Slide Valve
{{steam engine configurations Engine valves

Use

Murdoch's D slide valve

Balanced slide valve

See also

External links