Downloaded from https://www.everyspec.com FM 1-509 Pressure is the force applied to one unit of area--usually 1 square inch. For example, the pressure on a piston head develops the force that operates a mechanism. In this manual, pressure is measured in pounds per square inch (psi). If any two of the above factors are known, the third can be computed by using the equation in Figure 1-1. To apply this equation, multiply the two lower factors together to get the top factor; then divide the top factor by the known lower factor to get the unknown lower factor.
If the area in square inches and the pressure in psi are known, simply multiply the area (A) times the pressure (P) to obtain the force (F) in pounds. Similarly, if the force in pounds and the area in square inches are known, divide F by A to obtain P in psi. Finally, to obtain the area in square inches, divide F in pounds by P in psi. For example, a pressure of 50 pounds psi acts on a piston whose surface area is 5 square inches. What force is acting on the piston? Using the equation in Figure 1-1, multiply P (50 psi) times A (5 square inches) to obtain F. The answer is that a 250-pound force acts on the surface of the piston. Computing Volume, Area, and Length of Stroke.
The same type of triangular equation can be used to compute volume, area, and length of stroke. These terms, as used in hydraulics, are defined as follows: Volume is a measurement of quantity expressed in cubic inches. For example, the volume is the amount of liquid in a cylinder or the amount of liquid displaced by a pump or actuating cylinder. 1-4