HYDRAULIC PRESS. 367 HYDRAULIC RAM. ■nith water in one end of which works a plunger one inch square, and in the other end of which works a plunger twelve inches square, and we exert a pressure of one pound on the smaller plunger, this pressure will be transmitted un- diminished by the water, and will exert a total pressure of 1 X 12 X 12=144 pounds. The essentials of a hydraulic press are, there- fore, a small cylinder containing a plunger, to which pressure is applied, connected by pipe with a large cylinder containing a plunger, which . transmits the multiplied pressure to the object to be pressed or lifted. It is evident, further- more, that the two cylinders may be located any desired distance apart, the only limit being that
- .t which the pii)e and cylinder friction reduces
the available pressure for performing work below practicable amounts. (See Power. Tr.x.smis- siON OF.) In modern practice the pressure pump commonly feeds into a hydraulic accumulator (see AccuMUL-TOE) , and the press cylinder is operated from the accumulator and not directly from the pump. The construction of hydraulic presses varies with the purposes for which they .nre employed. Hydraulic presses for baling hay and cotton and expressing the oil from seeds, etc.. are built substantially as follows: Four iron pillars are erected at the corners of a hori- zontal square, and carry a cast-iron cap rigidly fastened to their tops. The under face of this cap forms the surface against which the material is pressed. At the bottom of the four pillars there is a similar casting which has a circular hole in the centre down through which passes the cylinder casting for the plunger. The plunger has an upward motion in the act of pressing, and carries on its top a head or platen consisting of a square casting. The material to be pressed is placed between the lower face of the top casting and the upper face of the platen. Often a boxing is placed around the four sides of the .space in which the head moves to nrevent the material being pressed from squeezing out laterally. The ronstruction of n press for hydraulic forging differs from the above as follows: The cylinders and plungers are carried by the top casting or column cap and the plungers work downward in the act of pressing; the bottom casting carries the anvil; the plungers carrj' a die for the head; and two or more cylinders are provided for raising the plunger and die for a fresh stroke. Generally, also, two pressure plungers and cylin- ders are employed instead of one. Forging presses are made of all sizes, from that required in pressing out articles like revolver cartridge eases to those used in forging steamship shafts and armor plates, .rmor-plate presses having a capacity of 14.000 tons are in use. HYDRAULIC PRESSURE ENGINE. A motor in which water is made to do work by means of its pressure only acting on a piston or plunger reciprocating in a cylinder, or, in some cases, on a revolving piston similar to those employed in a rotary steam-engine. In the case of a turbine the pressure of a column of water is, in the first instance, employed in giv- ing motion to the fluid itself, and after this mo- tion has been produced the energy due to it is utilized in doing work. In the case of the pres- sure engine the only pressure expended in giving motion to the fluid is that needed to make the water follow the piston and escape from the mo- tor, and to secure efficiency this piston should be as small as practicable. This end is most nearly secured when the pressure is great and the speed of the engine is low. The first pressure engine was designed by Sir William Armstrong (q.v.), and was of the rotary type. This engine was never actually used, and was replaced by a re- ciprocating engine designed by the same engineer. Since Sir William .Vrmstrong's invention a great variety of hydraulic pressure engines have been invented, the majority of which are of the re- ciprocating type. Hydraulic pressure engines are particularly adapted to the use of high-pressure water in comparatively small quantities, and where these conditions prevail they have a con- siderable field of usefulness, particularly as sec- ondary motors for operating mechanical con- trivances, such as the opening machinery for swing bridges, cranes, hoists, etc. For further information consult Bodmer, Hydraulic Motors, Turbines, and Pressure Engines (New York, 1889). See Tt-RBIXE. 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 suflicient 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 compresses 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- /Ftsifhn when Open ■<-. '■Rubber Pure Water Pipe ^•Waste Valve BIFE HTDBAUI.IO EAII. vation. A sniffing 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 hei.ffhts in like proportion; but some water is wasted during each cycle, and there is more or less friction to be overcome, depending on the de- sign of the ram and the length and diameter of the pipes. An efficiency of 75 per cent, would be high. With the increase in the ratio of the fall nf the drivins water to the elevation to he overcome, the efficiency decreases, particularly
