Technical Guide
DAN-LIQ-TG-44-rev0813
November 2013
5
Pressure Defined:
In order to determine the total force exerted on a surface, it is necessary to know the pressure or force on a unit of area. We
usually express this pressure in “Pounds per Square Inch”, abbreviated psi. Knowing the pressure and the number of square
inches of area on which it is being exerted, one can readily determine the total force.
(Force in Pounds = Pressure in psi x Area in Sq. In.)
How Pressure is Created:
Pressure results whenever the flow of a fluid is resisted. The resistance may come from (1) a load on an actuator, (2) a control
valve or, (3) a restriction (or orifice) in piping. See Figure 1-3.
As flow is restricted by
closing the manual valve...
With the manual valve
closed...
... pressure builds up.
... the pressure gauge reads the
maximum pressure available.
25 psi
50 psi
PUMP
PUMP
When the manual valve is
wide open, all flow is
unrestricted.
There is no pressure in this condition.
0 psi
5 gpm
PUMP
PRESSURE CAUSED BY RESTRICTION AND LIMITED BY PRESSURE CONTROL VALVE.
Figure 1-3
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