Four mounted photographs of open topped single acting pumping engine

Four mounted photographs of open topped single acting pumping engine, early 19th century, 24 ins diam. by 5 ft stroke at Philadelphia Pit, Gildersome near Leeds, framed and exhibited

This beam engine resembles in construction James Watt's single-acting engine, with steam only being admitted to push the piston downwards, except that the cylinder is open-topped and in consequence the piston acts by atmospheric pressure only. This permits some simplification in the valve gear, since Watt's equilibrium valve (which transferred exhaust to beneath the piston after it had worked above it) is dispensed with, but at the cost of increased steam consumption.