The Caprotti valve gear is a type of steam engine

Steam engine

A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...

 valve gear

Valve gear

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 steam to escape, respectively, at the correct points in the cycle...

 invented in the early 1920's by Italian

Italy

Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

 architect and engineer Arturo Caprotti

Arturo Caprotti

Arturo Caprotti was an Italian engineer and architect. In 1915 or 1916 he invented the Caprotti valve gear rotary cam poppet valve gear for steam engines of all kinds, but in practice it was employed almost exclusively in railway locomotives.-External links:* at www.steamindex.com...

. It uses camshaft

Camshaft

A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...

s and poppet valve

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...

s rather than the piston valve

Piston valve

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.Examples of piston valves are:...

s used in other valve gear. While basing his design on automotive valves, Caprotti made several significant departures from this design to adapt the valves for steam.

In the 1950s, Caprotti valve gear was improved and this British Caprotti valve gear was fitted to the last two British Railways-built 'Black Fives'

LMS Stanier Class 5 4-6-0

The London Midland and Scottish Railway's Class 5 4-6-0, almost universally known as the Black Five, is a class of steam locomotive. It was introduced by William Stanier in 1934 and 842 were built between then and 1951...

 44686/7

LMS Stanier Class 5 4-6-0 44686/7

The last two of the 842 LMS Stanier Black Fives, numbers 44686 and 44687 were constructed by British Railways at Horwich Works in 1951.- Overview :...

, the last 30 BR standard class 5

BR standard class 5

The British Railways Standard Class 5MT 4-6-0 was one of the standard classes of steam locomotives built by British Railways in the 1950s. 172 were built, essentially being a development of the LMS Stanier Class 5 4-6-0 .- Background :...

s, numbers 73125-54 and the unique BR standard class 8 71000 Duke of Gloucester. Results were mixed, with the performance of the Duke of Gloucester particularly disappointing but this was later found to be due to errors elsewhere in the design and construction.

Although more expensive to manufacture than its rivals, this improved Caprotti valve gear is considerably more efficient than any other. Benefits include much of the mechanism enclosed thus leading to reduced wear and tear from the harsh steam locomotive environment and completely independent control of admission and exhaust. The restored Duke of Gloucester, with its flaws eliminated, has proved the concept.

External links

• British Caprotti Valve Gear on the Duke of Gloucester
• A history of British Caprotti valve gear.