The Corliss mill engineGeorge H. Corliss of Providence, Rhode Island · patented 1849
An American answer to an American problem: cotton mills where a flutter in speed snapped a thousand threads, and coal that cost real money. Corliss gave each cylinder four separate rocking valves worked from a wrist plate, and — the masterstroke — handed the cutoff itself to the governor, so the engine answers a changing load with full-pressure steam admitted for exactly as long as needed, never strangled through a half-shut throttle. Strengths: speed held within a hair, superb economy at part load, hot and cold passages kept apart. Weaknesses: a watchmaker's worth of trip gear, and release mechanisms that set a ceiling on speed. So confident was Corliss that he offered to be paid from the coal his engines saved. Drag the mill load about and watch the cutoff answer while the needle barely stirs.
Key to the plate
a. — from the boiler house. The boiler moves out of the picture: a mill engine of this size is fed by a battery of boilers in their own house, and the steam main enters at the wall. The gauge glass and feed cocks on the panel keep their water all the same.
b. — governor & trip gear. The flyballs no longer strangle the steam at a throttle — they work the trip gear, deciding afresh each stroke when to release the valves and cut the steam off. Full boiler pressure always, admitted briefly: speed held within a hair, and economy with it. This is the whole Corliss idea.
c. — Corliss valves & wrist plate. Four rocking cylindrical valves, one per port, danced by the wrist plate — hot steam enters through passages the cold exhaust never touches, which spares the charge that wall-chill used to steal. The trip lets each admission valve snap shut on its dashpot the instant the governor says enough.
d. — crosshead & guides. The engine lies down: no beam, no parallel motion — the piston rod runs straight to a crosshead sliding in machined guides, and a connecting rod turns the crank. Horizontal, low, and stiff: the pattern every mill engine follows for the next sixty years.
e. — fly-wheel. Broad enough to double as the mill’s belt pulley: the wheel is the power take-off, driving line shafting through leather belts to a thousand spindles. Eleven hundred threads notice every tremor it fails to iron out.