THE HYDRAULIC PRESS.
The hydraulic press consists of1. A Lever,2. A Pump,3. and a Ram working in a4. 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 atMin 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 pipea.
Fig. 146.
Fig. 146.
Water is delivered from the pump A through a heavy lead pipe into the cylinderBof the hydraulic press. The ram P is made tight by the leather packingnand has a table or platform attached to its upper end as shown. The stationary partQconsists of a heavy cast-iron plate supported by four wrought-iron or machinery steel columns. By operating the handleMof 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. 146shows an enlarged section of the pump used in connection with this press. When the plungerPrises a partial vacuum is formed below it and the suction valveOrises allowing the pump barrel to fill with water through the strainer and suction pipe in the cistern.
When the plunger descends the valveOcloses and the water passes through the discharge valvehinto the pipeK, thence into the cylinderBof the press where it acts upon the ram. When the press has done its work the ram may be lowered by opening the relief valver. The safety valve is shown ati. By removing the plughthe discharge valve can be reached to grind it in when necessary.
Note.—Hydraulic Pressure Transmission.Water under high pressure—500 to 3000 lbs. per square inch and upwards—affords a very satisfactory method of transmitting power to a distance, especially for the movement of heavy loads at small velocities, as by cranes and elevators. The system consists usually of one or more pumps capable of developing the required pressure; 2, accumulators, described on thenext page; 3, the distributing pipes, and 4, the presses, cranes, or other machinery to be operated. This property of fluids invests us with a power of increasing the intensity of a pressure exerted by a comparatively small force, without any other limit than that of the strength of the materials of which the engine itself is constructed. It also enables us with great facility to transmit the motion and force of one machine to another, in cases where local circumstances preclude the possibility of instituting any ordinary mechanical connection between the two machines. Thus, merely by means of water-pipes, the force of a machine may be transmitted to any distance, and over inequalities of ground, or through any other obstructions.
Note.—Hydraulic Pressure Transmission.Water under high pressure—500 to 3000 lbs. per square inch and upwards—affords a very satisfactory method of transmitting power to a distance, especially for the movement of heavy loads at small velocities, as by cranes and elevators. The system consists usually of one or more pumps capable of developing the required pressure; 2, accumulators, described on thenext page; 3, the distributing pipes, and 4, the presses, cranes, or other machinery to be operated. This property of fluids invests us with a power of increasing the intensity of a pressure exerted by a comparatively small force, without any other limit than that of the strength of the materials of which the engine itself is constructed. It also enables us with great facility to transmit the motion and force of one machine to another, in cases where local circumstances preclude the possibility of instituting any ordinary mechanical connection between the two machines. Thus, merely by means of water-pipes, the force of a machine may be transmitted to any distance, and over inequalities of ground, or through any other obstructions.