Troubleshooting guide

57
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FREE SPRING – FREE AIR
The energy of compressed air is best compared to the
energy of a coiled spring. Figure 8 shows a coiled spring
in its free position and air in its free or atmospheric state.
COMPRESSED SPRING – COMPRESSED AIR
When the spring is compressed, as shown in Figure 9,
energy is stored in it. Stored energy is the same result
when free air is compressed. This energy can be used to
do work. And, due to the fl exibility of air, this energy can
be stored in a relatively small space.
See Figure 10, showing two connected reservoirs. If one
contains air above atmospheric pressure and the
other contains air at atmospheric pressure, air will
fl ow from the reservoir with the higher pressure until
the pressures in both reservoirs equalize. Flow will
also stop if it is interrupted by some outside force, such
as the closing of a valve in the connecting line. This is
similar to the action of liquids, except that pressure is the
controlling medium. In liquids, gravity would ordinarily be
the controlling medium.
We noted earlier that normal atmospheric air is at a
pressure of 14.7 psi. In Figure 11, the reservoir on the
right has a volume of six cubic feet. When another six
cubic feet of air is added into it, the gauge pressure of the
air in the reservoir – which originally read zero – will rise
to 14.7 psi. It follows that each time a quantity of free air
equal to the volume of the reservoir is forced into it, the
gauge pressure will rise another 14.7 psi.
In Figure 12, we see a piston with an airtight chamber
behind it. When compressed air enters the chamber, it will
cause the piston to move until it encounters a resistance
equal to the force developed by the compressed air.
Because the air pressure is based on pounds per square
inch, it follows that the compressed air will develop a
force in pounds on the movable object equal to the
product of the air pressure multiplied by the effective area
of the movable object. For example, consider a piston
or a fl exible diaphragm in a brake chamber having an
area of 10 square inches. If air at fi ve pounds per square
inch pressure is acting on the piston or diaphragm, the
developed force will be 50 pounds. Similarly, if air at a
pressure of 10 pounds per square inch is acting upon it,
a force of 100 pounds will be developed.
FIGURE 12 - FUNDAMENTALS OF COMPRESSED AIR
FIGURE 13 - FUNDAMENTALS OF COMPRESSED AIR
Properties of Compressed Air (continued)
Where Supply B
pressure is greater
than Supply A
pressure
Where Supply A
pressure is the same
as Supply B pressure