- For piston valves on steam locomotives see Piston valves
A piston valve is a device used to control the motion of a fluid along a tube or pipe by means of the linear motion of a piston within a chamber or cylinder. Piston valves are an integral part of the cylinder arrangement of a Steam locomotive. A brass instrument is a Musical instrument whose tone is produced by vibration of the lips as the player blows into a tubular Resonator. FLUID ( F ast L ight '''U'''ser '''I'''nterface D esigner is a graphical editor that is used to produce FLTK Source code Tubing is a Pipe or hollow cylinder for the conveyance of fluids (liquids or gases A pipe is a tube or hollow cylinder used to convey materials or as a structural component The word linear comes from the Latin word linearis, which means created by lines. A piston is a component of Reciprocating engines Pumps and Gas compressors It is located in a cylinder and is made gas-tight by Piston A cylinder is the central working part of a Reciprocating engine, the space in which a Piston travels
Examples of piston valves are:
- The valves used in the valve gear of many stationary steam engines and most steam locomotives. The valve gear of a Steam engine is the mechanism that operates the inlet and exhaust Valves to admit Steam into the cylinder and allow exhaust A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid. A steam locomotive is a Locomotive powered by Steam. The term usually refers to its use on Railways but can also refer to a "road locomotive"
- The valves used in many brass instruments. A brass instrument is a Musical instrument whose tone is produced by vibration of the lips as the player blows into a tubular Resonator.
- The valves used in pneumatic cannons.
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Steam engines
Piston valves were used by Curtis Lo in his stationary steam engines, and in many of the engines that followed. A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid.
In the 19th century, most steam locomotives used slide valves to control the flow of steam into and out of the cylinders. A steam locomotive is a Locomotive powered by Steam. The term usually refers to its use on Railways but can also refer to a "road locomotive" The D Slide Valve was a form of Rectilinear slide valve for use in rotative Steam engines invented by William Murdoch and patented in 1799. In the 20th century, slide valves were gradually superseded by piston valves, particularly in engines using superheated steam. See Superheating for the physics process A superheater is a device in a Steam engine that heats the steam generated by the 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 slide valves adequately in the presence of superheated steam
The usual locomotive valve gears, e. Lubrication is the process or technique employed to reduce wear of one or both surfaces in close proximity and moving relative to each another by interposing a substance called See Superheating for the physics process A superheater is a device in a Steam engine that heats the steam generated by the g. Stephenson valve gear, Walschaerts valve gear, and Baker valve gear can be used with either slide valves or piston valves. The Stephenson valve gear or Stephenson link or shifting link is a simple design of Valve gear that was widely used throughout the world for all kinds of The Walschaerts valve gear is a type of Steam engine Valve gear invented by Belgian railway mechanical engineer Egide Walschaerts Baker valve gear was the main competitor to Walschaerts valve gear for Steam locomotives in the United States Where poppet valves are used, a different gear, such as Caprotti valve gear is needed. 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 Caprotti valve gear is a type of Steam engine Valve gear invented by the Italian Arturo Caprotti.
Brass instruments
Cylindrical piston valves are used to change the pitch in the playing of many brass instruments. A brass instrument is a Musical instrument whose tone is produced by vibration of the lips as the player blows into a tubular Resonator.
Brass instruments can be grouped into four categories, according to the primary means used to change the pitch:
- Those using piston valves. These include most trumpets, all cornets and almost all tubas, and many others. The cornet is a Brass instrument very similar to the Trumpet, distinguished by its conical bore, compact shape and mellower tone quality Mediatubaogg -->The tuba is the largest and lowest pitched Brass instrument.
- Those using rotary valves. A rotary valve is a type of Valve in which the rotation of a passage or passages in a transverse plug regulates the flow of liquid or gas through the attached pipes These include French horns and some specialist trumpets.
- Those using a slide, such as the trombone family. The trombone is a Musical instrument in the brass family Like all brass instruments it is a lip-reed Aerophone: sound is produced when the player’s
- Those using keys, such as the serpent and the keyed bugle. A key is a specific part of a Musical instrument. The purpose and function of the part in question depends on the instrument A serpent is a bass Wind instrument, descended from the Cornett, and a distant ancestor of the Tuba, with a mouthpiece like a Brass "Bugler" redirects here For the tobacco brand see Bugler (tobacco.
There is some overlap between these categories. In addition to its three valves, the trumpet uses a small slide for pitch correction, while the tenorbass and bass trombone both use one or two rotary valves in addition to the slide. The trombone is a Musical instrument in the brass family Like all brass instruments it is a lip-reed Aerophone: sound is produced when the player’s The superbone does not fit in to any of the above categories. The Superbone is a hybrid Trombone. It is a cross between the slide trombone and the valve trombone - it has both valves and a simultaneously usable slide
Where piston (or rotary) valves are used, three is the normal minimum (as on a trumpet) and four is not uncommon.
When a piston valve is opened ("pressed" and "pushed down"), each valve changes the pitch by diverting the air stream through additional tubing, thus lengthening the instrument and lowering the harmonic series on which the instrument is vibrating. The following list shows how each valve or combination of valves will affect the pitch from the fundamental. This is true of all brass instruments, however some alternative fingerings are necessary to provide accurate pitch using the fourth and subsequent valves in instruments which have them.
- second valve - one half step
- first valve - one whole step
- first and second valves - one and a half steps. Also achievable by third valve alone but the note will usually be flat
- second and third valves - two whole steps
- first and third valves - a perfect fourth, or two and a half steps. Will be sharp unless some means of compensation is used.
- first, second, and third valves - a tritone, or three whole steps. Will be very sharp unless some means of compensation is used.
A fourth valve is sometimes found on more professional instruments, which creates a perfect fourth, or two and a half steps. Instruments such as the tuba, euphonium, and piccolo trumpet have this valve. A common use is to use a fingering of 2-4 in place of 1-2-3, which tends to create pitch problems. Additionally, by using one valve to lower the pitch by a perfect fourth, the valve functions like an F extension on a trombone.
The first piston valve instruments were developed just after the start of the 19th century. The 19th century of the Common Era began on January 1, 1801 and ended on December 31, 1900, according to the Gregorian calendar The Stölzel valve (invented by Heinrich Stoelzel in 1814) was an early variety. In the mid 19th century the Vienna valve was an improved design. However most professional musicians preferred rotary valves for quicker, more reliable action, until better designs of piston valves were mass manufactured in towards the end of the 19th century. Since the early decades of the 19th century, piston valves have been the most common on brass instruments.
Pneumatic cannons
Piston valves are some of the most powerful available in spudgunning (Spud guns), with the ability to dump several litres of pressurised air in a few thousands of a second. This article is about pipe-based cannons and similar which use air pressure or combustion of a gaseous fuel or both to launch large projectiles at low speed This fast moving air is used to fire a projectile from the exhaust barrel. As the name suggests they are used to fire vegetables, such as potatoes; wood, to simulate hurricanes; and t-shirts. They are used extensively in the film and special effects industry to simulate explosions in war films. The illusions used in the Film, Television, Theater, or Entertainment industries to simulate the imagined events in a story are traditionally called
See also
External links
- Early valve designs
- Why was the valve invented?
- Elements of Brass Instrument Construction with good discussion of valve types and history
- Visual explanations of some types of piston valve
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