Drawing of James Watt's Rotary and Semi-Rotary Engines

Drawing of James Watt's Rotary and Semi-Rotary Engines 1782

This is copied from Watt's patent specification of 1782; in James Watt's workshop from his home at Heathfield outside Birmingham, however, there is an unfinished model of this engine, which was commenced in 1765 or 1766 (See Inv No 1924-792). The engine has a short horizontal cylinder with a radial piston which can swing through an arc of 240 deg. The lower sector of the cylinder is fitted with a stationary abutment block through which steam is admitted to either side of the piston alternately. Below the cylinders are valve boxes for the distribution of the steam, while beneath these is a jet condenser, and two air pumps which are driven by racks from a pinion on the vibrating shaft. A large spur wheel on this shaft has two racks gearing with it, and these move the rods of the two pit pumps that the engine was designed to work; by this latter arrangement the pump rods mutually counterbalance.