[Illustration: FIG. 144.] [Illustration: FIG. 145.]
1. A Lever, 2. A Pump, 3. and a Ram working in a 4. Cylinder.
Bramah in the year 1796 brought out a very interesting apparatus which illustrates the law of the equality of pressure which has been widely adopted in the practical use of the hydraulic press. The principle upon which this press works is due to Pascal but it remained for Bramah to put it to practical use. Enormous pressures are developed by operating the hand lever shown at _M_ in Fig. 145, which is connected with pump plunger P. The pump barrel A is very thick and receives its supply from the cistern H through the suction pipe _a_.
Water is delivered from the pump A through a heavy lead pipe into the cylinder _B_ of the hydraulic press. The ram P is made tight by the leather packing _n_ and has a table or platform attached to its upper end as shown. The stationary part _Q_ consists of a heavy cast-iron plate supported by four wrought-iron or machinery steel columns. By operating the handle _M_ of the pump any substances placed between the table on the ram P and the plate Q may be compressed to any reasonable extent.
The pressure which can be obtained by this press depends on the relation of the ram P to that of the plunger P. If the former has a transverse section fifty or a hundred times as large as the latter, the upward pressure on the ram will be fifty or a hundred times that exerted upon the pump plunger. By means of the lever M an additional advantage is obtained.
If the distance from the fulcrum to the point where the power is applied is five times the distance from the fulcrum to the plunger P the pressure on it will be five times the power. Thus, if a man acts on M with a force of sixty pounds, the force transmitted by the plunger P will be 300 pounds, and the force which tends to raise the ram will be 3,000, supposing the section of ram is a hundred times that of the pump plunger.
Over-pressure, is prevented by safety-valve shown in front of the pump A. Fig. 146 shows an enlarged section of the pump used in connection with this press. When the plunger _P_ rises a partial vacuum is formed below it and the suction valve _O_ rises allowing the pump barrel to fill with water through the strainer and suction pipe in the cistern.