HYDRAULIC RAM. Primarily, a device by which the momentum of water flowing by gravity in a pipe is utilized to lift a portion of itself through another pipe to an elevation greater than the source of supply. The flow of water in the main or drive pipe is automatically checked by the closing of a valve at its foot. When the valve is open the water escapes freely and flows to waste, but very soon a sufficient momentum is attained to close the valve. The confined water then lifts another valve, opening into an air-chamber mounted over the foot of the drive-pipe. The water partially fills this cham ber, and in so doing compreEss the air therein until the pressure in the chamber just balances that of the column of water in the drive-pipe. The valve at the foot of the drive-pipe then opens, and the process is repeated. The pressure of the compressed air in the air-chamber forces the water in the bottom of the chamber out through a small supply pipe to the desired ele vation. A snifting valve is provided to supply air to the chambers to make good the losses due to absorption of air by the water. Theoretically, 100 gallons of water falling 15 feet would raise 15 gallons 100 feet, and other quantities and heights in like proportion: hut sonic water is wasted during each cycle, and there is more or less friction to he overcome, depending on the de sign of the ram and the length and diameter of the pipes. An efficiency of 75 per cent. would he high. With the increase in the ratio of the fall of the driving water to the elevation to he • overcome, the efficiency decreases, particularly when the ratio exceeds 1-12 (i.e. 1 foot fall for
feet raised). Where the fall is great, the Wear turd tear on the rain is exeessiVe. Solite au• thorities give the desirable working limit for a hydraulic. rani as I to 10 feet fall of drive water and a lift of not over 250 feet, hut with so great a lift a large proportion of the water will be wasted. The ram, described, was in vented by Joseph :tlichael de of France, in 1790; but in 1772 an Englishman named John •hitehurst built a machine embody ing the same principle, except that the valve at the foot of the drive-pipe had to be dosed by band. Ilis device was described in the Phi/u sophiral Transactions for 1775. Many improve ments have been made in the maehine of Mont goltier, the most important of which, perhaps, aim to lessen the shock of the operation of the Springs have lieen used to that end; the drive-pipe valve has been counterweighted, and a portion of the air compressed in the chamber has been used to drive a small air-motor, so con nected as to aid in the gentle dosing of the valve at each cycle. Another improvement is the equipment of rains so that a supply of dirty water may lie used to lift clean water, either when the supply of the latter is scanty. or is not available under a sufficient head. Finally. hy draulic rams are WWII to drive pumps, when they are properly classed under pumping engines. See Pumrs AND lumpiNo MACHINERY.