Michael Frankel, CIPE
Utility Systems Consultants, Somerset, NJ
Compressed air is an often-used utility system found in facilities. It is used to do
work by producing linear motion and actuation through a piston and cylinder or
a diaphragm for air-actuated valves, doors, dampers, brakes, and so forth. Atomizing
and spraying as well as providing the moving force for hard-to-pump fluids are
other applications. Compressed air can be bubbled up to measure fluid levels,
agitate liquids, and inhibit ice formation in bodies of water. Air circuits also satisfy
complex problems in automatic control, starting/stopping, and modulation of valves
in machines and processes. This chapter will discuss centrally distributed compressed
air piping used in various types of facilities for light industrial and control purposes.
Compressed gases for laboratories are discussed in Chap. C16.
Air is a fluid. The two types of fluids are liquids and gases. A gas has a weaker
cohesive force holding its molecules together than does a liquid. Air is a mixture
of gases, and its main components are oxygen and nitrogen, with many other gases
in minor concentrations. Air is the standard from which specific gravity is calculated,
and which can be found by dividing the molecular weight of the subject gas into
the molecular weight of air (which is 29).
The actual solid volume that the atomic structure of gas occupies in relation to
the total volume of a gas molecule is quite small, so gases are mostly empty space.
This is why gases can be compressed. Pressure is produced when molecules of a
gas in an enclosed space rapidly strike the enclosing surfaces. If this gas is confined
into a smaller and smaller volume, molecules strike the container walls more fre-
quently, producing a greater pressure.
DEFINITIONS AND PRESSURE MEASUREMENTS
Definition of Compressed Gases
A compressed gas is any gas stored or distributed at a pressure greater than atmo-