By Julius de Waal

Musgrave's non-dead-centre engine was a stationary steam engine of unusual design, intended to solve the problem of stopping on dead centre. It was designed in 1887 to serve as a marine engine and used a pair of linked cylinders to prevent the engine from stopping in a position where no turning force could be applied. At least one engine is known to survive, the Park Street Mill Engine in the Bolton Steam Museum (below).

The 'dead centre' of a piston engine with cranks is when the piston is at the exact top or bottom of the stroke and so the piston cannot exert any torque on the crankshaft. If a steam engine stops on dead centre, it will be unable to restart from that position.

Several solutions have been applied. One of the simplest is to try not to stop in this position, the crudest to apply a strong arm with a crowbar to turn the engine over a little. Small steam barring engines were also used to move the engine away from dead centre before starting. If the engine has multiple cylinders, most geometries for these are arranged so that all cylinders are never at dead centre together and so one may always be used for starting.

Musgrave's solution was more complex: using two cylinders, additional connecting rod linkages, and geometry to avoid the problem.

John Musgrave & Sons of the Globe Ironworks, Bolton was a mill engine builder, supplying the local cotton mills. He licensed the design in 1892, then patented further improvements to it in 1893.

Musgrave built up to 50 of these engines, the largest offering 1,500 ihp with quadruple expansion working. Ten of these quadruple expansion, four cylinder engines were built, the remainder mostly being two-cylinder compound engines, as the Park Street Mill engine. The larger engines used Corliss valves.

The non-dead-centre mechanism also evened-out power as the crank rotated, making it suitable for driving dynamos for electricity generation. The engine also had relative high speed for its day, making it possible to drive dynamos directly. A 500 hp Corliss valve engine was installed for electricity generation in Southport.

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This version is in imperial - metric version here.