HANDLE
PISTON 2
PISTON 1
CYLINDER 2
CYLINDER 1
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Figure 8-1.--Transmission of force by liquids.
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
A. TRANSMITTED FORCE THROUGH FLUID
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.
Multiplication of Forces
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
B. TRANSMITTED FORCE THROUGH SMALL PIPE
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
Figure 8-2.--Force transmitted from piston to piston.
2, a downward force of 20 pounds acting on piston 1
8-2
