Exhaust Valves
  1. Exhaust valve from 71000
  2. The cage in which it operates
  3. Exhaust valve from a contemporary diesel locomotive (Class 47)
  4. Exhaust valve from a Rover motor car (3500 V8)
British Caprotti Camshaft Assembly The sectioned original centre cylinder on display at the Science Museum, Kensington in 1978. This is now known as the Caprotti Demonstration Gear.

In 1911, Arturo (Arthur) Caprotti, a student of automobile engineering at Milan University, was told by his tutor that the steam railway locomotive was THE most inefficient machine. The reasons were:

Caprotti transferred the principle of the poppet valve from the motor car to the steam railway engine:

His invention was brilliant but flawed. The British Development of the valve gear, brought major changes in the poppet valves themselves, and in 1950 Tom Daniels, Chief Engineer for Associated Locomotive Equipment, changed the camshaft design to include two exhaust cams instead of one, which could be moved (mechanically) in relation to each other, like the inlet cams, thus achieving complete variable valve actuation.

How Variable Valve Actuation Works

Ironically, in this decade, some motor car manufacturers, including Mercedes and Honda, have succeeded in applying some of the British Caprotti principles to new camshaft designs in motor car engines, albeit electronically controlled and hydraulically induced.

The new Jaguar 3 litre AJ-V6 engine features what is described as a - "sophisticated camshaft phasing system", also under the control of the engine management module, further helps to optimise torque output, particularly at mid and high engine speeds. Engine torque output is optimised by advancing or retarding the opening and closing of the inlet valves at different engine speeds. This benefits fuel economy, emissions control and engine idle quality, as well as performance.

Perhaps now they should all be seeking to imitate some of the other British Caprotti design features?

Kind permission has been given by The National Railway Museum for the exhibit shown right (original centre cylinder, cambox and reversing gear), which was exhibited at The Science Museum in Kensington until 1997, to be loaned to The West Somerset Railway Association. This will be exhibited at the Bishops Lydeard Visitor Centre, West Somerset Railway, from the beginning of the 2002 season.

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