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. The common stopcock is the simplest form of rotary valve. Rotary valves have been applied in numerous applications, including:
- Changing the pitch of brass instruments.
- Controlling the steam and exhaust ports of steam engines, most notably in the Corliss steam engine.
- Periodically reversing the flow of air and fuel across the open hearth furnace.
- Loading sample on chromatography columns.
- Certain types of two-stroke engines.
- Most hydraulic automotive power steering control valves.
Use in brass instruments 
Joseph Riedl is credited with the first use of rotary valves on brass instruments in 1832.
Use in industry 
In industry, a rotary valve (which can also be called airlock) is often used to enter or extract material from two chambers with different pressure level.
As part of the material exchange process, the valve is often used as a measuring or metering device.
Use in engine design 
The rotary valve combustion engine possesses several significant advantages over the conventional assemblies, including significantly higher compression ratios and rpm, meaning more power, a much more compact and light-weight cylinder head, and reduced complexity, meaning higher reliability and lower cost. As inlet and exhaust are usually combined special attention should be given to valve cooling to avoid engine knocking.
Rotary valves have been used in several different engine designs. In Britain, the National Engine Company Ltd advertised its rotary valve engine for use in early aircraft, at a time when poppet valves were prone to failure by sticking or burning.
Austrian engine manufacturer Rotax used rotary intake valves in their now out-of-production 64 hp (48 kW) Rotax 532 two-stroke engine design and continues to use rotary intake valves in the 532's successor, the current-production 64 hp (48 kW) Rotax 582.
US company Coates International Ltd has developed a spherical rotary valve for internal combustion engines which replaces the poppet valve system. This particular design is four-stroke, with the rotary valves operated by overhead shafts in lieu of overhead camshafts (i.e. in line with a bank of cylinders). The first sale of such an engine was part of a natural gas engine-generator.
Rotary valves are highly suitable for high reving engines, such as those used in sportscars and F1 racing cars, on which traditional poppet valves with springs can fail due to spring resonance and where the desmodromic valve gear is too heavy, large in size and too complex to time and design properly. Rotary valves allow for a more compact and lightweight cylinder head design. They rotate at half engine speed and lack the inertia forces of reciprocating valve mechanisms. This allows for higher engines speeds offering appr. 10% more power. The 1980s MGN W12 F1 engine used rotary valves but never raced. Between 2002 and 2004 the Australian developer Bishop Innovation and Mercedes-Ilmor tested rotary valves for a F1 V10 engine.
'Bishop Innovations' patent for the rotary valve engine was bought out by BRV Pty Ltd, owned by Tony Wallis, one of the valves original designers. BRV has constructed several functional motors using the rotary valve technology, such as a Honda CRF 450, which had greater torque at both low(17% increase) and high (9% increase) engine speeds, and also produced more brake horsepower up to around 30% more at functional engine speeds. The engine was also considerably smaller and lighter, as the cylinder head assembly was not as large.
Use in chromatography 
Rotary valves are used for loading samples on columns used for liquid or gas chromatography. The valves used in these methods are usually 6-port, 2-position rotary valves.
See also 
- Flight magazine, April 1911
- Aspin Rotary Valve Engine Accessed on 18th Oct 2010
- Free engine info Accessed on 18th Oct 2010
- BRP-Rotax GmbH & Co. KG (2006). "OPERATORS MANUAL FOR ENGINE TYPES 447, 503 & 582". Retrieved 4 January 2011.
- Raisner, William: LEAF catlog, pages 6-105. Leading Edge Airfoils, 1995.
- Coates International Accessed on 3rd Mar 2011
- RCV. "RCV Engines Ltd - UK (India – AutoExpo 2004)". Retrieved 2012-01-03.
- Keith Lawes. "The Rotating Cylinder Valve 4-stroke Engine (SAE Paper 2002-32-1828)". Retrieved 2012-01-03.
- Tony Wallis. "The Bishop Rotary Valve (AutoTechnology, Special 2007)". Retrieved 2011-12-26.
- "The Bishop Rotary Valve". AutoTechnology Magazine. Retrieved 19 April 2012.