Tandem Compound Mill Engine
Based
on the 1894 Roberts Brothers (Nelson, Lancs.) “Peace” engine in the
Queen Street Cotton Mill Museum, Burnley, Lancashire.
Running at 68 RPM, this single 500 HP engine powered the entire mill, simultaneously driving over 1,100 looms and other machines via belts, pulleys and 2,250 feet of shafting.
The 1:10 scale model demonstrates the action of the centrifugal governor and Dobson trip gear on the Corliss valves.
When
the crankshaft speed exceeds a preset limit, the centrifugal
weights
on the governor fly out and, via linkages, change the geometry of the arms
of the Dobson trip gear
on the HP cylinder.
Doing
so advances the cut-off point of the Corliss valves, reducing steam intake to
the HP cylinder (and indirectly to the LP cylinder), slowing the
engine.
The governor
weights then return to their normal position, and the
trip arms to theirs. The arms of the Dobson trip gear on the HP
cylinder have static adjustment only.
Because centrifugal force does not scale, on the model the action of the governor weights and linkages and the speed of the engine itself are manipulated by a mechanism concealed in the plinth, activating on a 30-second cycle.
For clarity, the handrails, oilers, guards, barring engine and steam pipes and conduits are not reproduced on the model. The Dobson trip units are approximately twice scale size.