The Hydraulic Press
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-139
2025-11-08
51
An important application of the principle stated in Pascal's Law is made in the hydrostatic or hydraulic press. Figure 1 shows a simple form in section. Two pistons or plungers A and B pass through water-tight collars into cylinders C and D. The piston A is moved by the lever F by applying the power at P. The body K to be compressed is placed between the platform G and a stationary framework H above it. The action is as follows: Both cylinders and the connecting tube E being full of water, the piston A is forced down, the pressure on the water C closing the valve d, and forcing the valve v open. The water displaced by A is forced through E, and passes into D, where it pushes B up, and compresses K. When the piston A is raised, the back pressure of B upon the water closes a; d opens, and water from some source of supply passes through it, keeping C full. The next stroke simply repeats the action. By. Pascal's Law, if base of cylinder B is 20 times as large as base of cylinder A, the pressure on it will be 20 times as great. This may be stated as follows : The pressure applied by the small piston: The pressure delivered to the large piston = The area of the small piston: The area of the large piston,
P: W = a: A = d2: D2,
d and D being the respective diameters of the two pistons. Since Pascal's Law applies to all liquids and since oil prevents. the rusting of the machine, oil is frequently used instead of water.
The fact that liquids are almost incompressible and perfectly elastic is of very great importance in connection with this machine. A pressure of 100 lb. to the square inch compresses water only.00033 of its original volume, and on the removal of the pressure, that volume is immediately restored.
The hydraulic press is largely used in such work as the compression of bales of cotton and other bulky materials for transportation on shipboard, where the space taken by a package of freight is a determining factor in the expense of carrying it.
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