Worthington Simpson Inverted Triple Expansion Engine
The engines consist of three cylinders with reheats between that expand the steam three times before it goes into the condenser. The cylinders are connected to a common crankshaft but each drives its own plunger pump below.
The engines were very reliable and efficient but with a high initial cost. They were designed to run 24/7 and often ran for 9 months at a time between maintenance operations. The engines were provided with steam at 200 psi and 180C, and consumed 13 tons of coal per day.
The three cylinders have areas such that they all do the same amount of work and are arranged 120 degrees out of phase from each other to balance the engine and provide a constant flow of water. On a down stroke water is pumped from the pump into the water main through a set of 52 one-way valves (in each unit) that open at slightly different times to give a smooth injection. On the up stroke the output valves close and a similar set of input ones open and water is sucked into the pump from the reservoir.
Each engine is 62 foot tall and weighs over 800 tons. They were built in situ from parts with a maximum weight of 16 tons each.