discovered the fundamental law for the science ofhydraulics. Pascal’s law tells us that pressure on aconfined fluid is transmitted undiminished in everydirection, and acts with equal force on equal areas,throughout the confining vessel or system.According to Pascal’s law, any force applied to aconfined fluid is transmitted in all directionsthroughout the fluid regardless of the shape of thecontainer. Consider the effect of this in the systemsshown in views A and B of figure 3-4. If there isresistance on the output piston (view A, piston 2) andthe input piston is pushed downward, a pressure iscreated through the fluid which acts equally at rightangles to surfaces in all parts of the container.If the force 1 is 100 pounds and the area of inputpiston 1 is 10 square inches, then pressure in the fluid is10 psi ( 100 ÷ 10). It must be emphasized that this fluidpressure cannot be created without resistance to flow,which, in this case, is provided by the 100-pound forceacting against the top of the output piston 2. Thispressure acts on piston 2, so for each square inch of itsarea, it is pushed upward with the force of 10 pounds.In this case, a fluid column of a uniform cross section isconsidered so the area of output piston 2 is the same asinput piston 1, or 10 square inches; therefore, theupward force on output piston 2 is 100 pounds—thesame as was applied to input piston 1. All that has beenaccomplished in this system was to transmit the 100-pound force around a bend; however, this principleunderlies practically all-mechanical applications offluid power.At this point, it should be noted that since Pascal’slaw is independent of the shape of the container, it isnot necessary that the’ tubing connecting the twopistons should be the full area of the pistons. Aconnection of any size, shape, or length will do so longas an unobstructed passage is provided. Therefore, thesystem shown in view B of figure 3-4 (a relativelysmall, bent pipe connects the two cylinders) will act thesame as that shown in view A.Multiplication of ForcesSome hydraulic systems are used to multiplyforce. In figure 3-5, notice that piston 1 is smaller thanpiston 2. Assume that the area of the input piston 1 is 2square inches. With a resistant force on piston 2, adownward force of 20 pounds acting on piston 1creates 10 psi (20 ÷ 2) in the fluid. Although this forceis much smaller than the applied forces in figure 3-4,Figure 3-4.—Force transmitted from piston to piston.the pressure is the same because the force isconcentrated on a relatively small area.This pressure of 10 psi acts on all parts of the fluidcontainer, including the bottom of output piston 2;therefore, the upward force on output piston 2 is 10pounds for each of its 20 square inches of area, or 200pounds (10 x 20). In this case, the original force hasbeen multiplied tenfold while using the same pressurein the fluid as before. In any system with thesedimensions, the ratio of output force to input force isalways 10 to 1 regardless of the applied force; forexample, if the applied force of input piston 1 is 50pounds, the pressure in the system is increased to 25psi. This will support a resistant force of 500 pounds onoutput piston 2.Figure 3-5.—Multiplication of force in a hydraulic system.3-3

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