Nortonthorpe Mills - steam engine, Corliss trip gear

Image: © Chris Allen Taken: 7 Oct 2006

This is on the high pressure cylinder of a Pollit and Wigzell tandem compound steam engine. The Corliss valve was a semirotary slide valve with two steam and two exhaust valves per cylinder. The steam valves were capable of being released and closed at various points before the end of the full stroke - this is termed cut-off and is under the control of the governor that moves a cam in the valve gear that forces apart two tripping surfaces, allowing the valve to be closed briskly by a spring with a cushioning dashpot. Different manufacturers used slightly different gears and this is recognisably that of Pollit and Wigzell of Sowerby Bridge. Another feature of this builder was the placing of the high and low pressure cylinders together to reduce length and having two low pressure piston rods, one either side of the high pressure. One of the low pressure piston rods passes horizontally in the lower quarter of the picture and its gland is seen to the right. The shiny vertical cylinder seen partly on the right hand edge is the low pressure steam chest safety valve.

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