HYDRAULIC WAGGON DROP.

93

the cage as it comes to the top of its stroke. This liolds thecage while the waggon runs on. When the cage with the Wag-gon on is required to descend, the catch-rod is liberated, andthen the valve handle is lifted. By the opening of this valve Jthe water passes from the bottom to the top of the piston, thusControlling the descent of the cage with the greatest nicety toany speed the attendant may choose. When the cage is at thebottom, a self-acting stop is removed by the action of the cagetouching the grouud, which allows the waggon to run off at thelower level. The cage being then lighter than the counter-weights, is drawn up again, the water in the cylinder, duringthe ascent, returning from the top to the bottom of the piston.When the cage arrives at the top of its stroke, it locks itself,and is then ready for another waggon to be run on.

The bulk of the water passes and re-passes through the coclcJ, but on account of the area of the piston being less on thelower side than the upper (by the area of the piston-rod on thelower side), the water at the top, displaeed as the piston rises,cannot find room at the lower side of the piston. and will tliere-fore find relief by a portion (equivalent to the cubical contentsof the piston-rod) passing through the small hole in the cylindercover into the supply tank. In the same way when the pistonagain descends, there would be an equal deficiency in the waterpassing from the bottom to the top side of the piston; this iscompensated for by the same amount of water re-passing throughthe hole in the cover. By this means the cylinder is alwayskept full of water, which is essential to the successful workingof the apparatus. It will be observed that the same water isused over and over again, and that the ball valve in the tankis merely to supply any loss from evaporation or leakage. Thesmall pipe 0, encircling the cylinder, is for the admission ofsteam in frosty weather to prevent the freezing of the water.This comes from the nearest steam or exhaust pipe, and aftercoiling a few times round the lower part of the cylinder, passesup to the top tank alongside of the connecting pipe.