HANDLE

PISTON 2

PISTON 1

CYLINDER 2

CYLINDER 1

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By Pascal's law, any force applied to a confined

If force 1 is 100 pounds and the area of piston 1 is

10 square inches (in.2), then the pressure in the fluid is

fluid is transmitted in all directions throughout the

2

10 pounds per square inch (psi) (100 lb ÷ 10 in.2 ). Take

fluid regardless of the shape of the container. Consider

22

the effect of this in the systems shown in views A and B

note that the fluid pressure cannot be created without

of figure 8-2. In view A, if there is resistance on the

resistance to flow, which in this case is provided by the

output piston (2) and the input piston (1) is pushed

100-lb force acting against the top of piston 2. This

downward, a pressure is created through the fluid,

pressure acts on piston 2 in such a way that for each

which acts equally at right angles to surfaces in all parts

square inch of its area, it is pushed upward with a force

of the container.

of 10 pounds. In this particular case, a fluid column of

uniform cross section is shown so that the area of

FORCE 2 -100 LBS.

FORCE 1 -100 LBS.

piston 2 is the same as that of piston 1. Therefore, the

upward force on piston 2 is 100 pounds, the same as

OUTPUT

PISTON 2

that applied to piston 1. All that has been accomplished

INPUT

10 SQ. IN.

PISTON 1

in this system is to transmit the 100-pound force

10 SQ. IN.

around a bend. However, this principle underlies

practically all mechanical applications of fluid power.

PRESSURE 10 LBS.

PER SQ. INCH

At this point you should note again that it is not

necessary for the tube connecting the two pistons to be

the full area of the pistons. A connection of any size,

shape, or length will do, as long as an unobstructed

passage is provided. Therefore, the system shown in

view B of figure 8-2 in which a relatively small, bent

FORCE 1 -100 LBS.

FORCE 2 -100 LBS.

pipe connects two cylinders will act exactly the same

as the system shown in view A.

PISTON 2

10 SQ. IN.

PISTON 1

10 SQ. IN.

PRESSURE 10 LBS. PER SQ. INCH

In figure 8-2, views A and B, the systems contain

pistons of equal area wherein the output force is

equal to the input force. Consider the situation in

figure 8-3, where the input piston is much smaller

than the output piston. Assume that the area of piston

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1 is 2 square inches. With a resistant force on piston

2, a downward force of 20 pounds acting on piston 1

8-2