Pneumatic Lifts
These lifts are now becoming common among blast-furnaces in different parts of the world, as compressed air is readily obtained from the blowing-engines which supply the furnaces. A wrought-iron cylinder, with its top end closed, somewhat longer than the distance to be travelled is suspended in a tank by counter-weights, after the manner of a gasometer. Air at three or four pounds above the atmospheric pressure is forced into the tank through a pipe. The load is lifted to the height required, and as the whole of the working parts are balanced, the amount of power required is only what will be sufficient to elevate the load. The return stroke is obtained by allowing the air to escape through a valve into the atmosphere, the empty wagon being weight sufficient to lower the bell in the tank. The motive power for the Gjers pneumatic lift is obtained from a pair of double-acting air-pumps, the lift being effected by the pressure of the atmosphere acting against a vacuum in a cylinder, the empty wagon being returned by the compression of air on the under side of the piston. See ELEVATOR.