An oil flow system that eliminates the need for an
oil circulating pump.
Compressed air is a powerful energy source which
is very useful in military and industrial applications. It
is of particular advantage in applications that require
intermittent power at some distance from its source, as
the air pressure can be maintained nearly constant at
work intervals. The rest of this chapter will pertain to
proper installation techniques of compressed-air
systems. When you are assigned a project that
includes compressed air lines, follow the prints and
Pressures and Uses
Compressed air usually falls into one of three
categories-power service, process service, or control
Power service is when compressed air either
moves something or exerts a force. Examples of power
service uses are pneumatic tool operation, air lifts,
clamps, and cylinders.
Process service is when compressed air is used as
part of the process itself. An example is the use of
compressed air in a combustion process. Compressed
air provides oxygen for the combustion, and, in turn, it
becomes a part of the combustion products and is no
longer identifiable as air.
Control purpose is when compressed air is used to
govern and/or regulate various equipment by
monitoring pressure or flow rates of some substance.
A pneumatically controlled combustion system is an
example of such an application.
Compressed air is distributed at low, medium, or
high pressure. A low-pressure system delivers air up to
125 psig. When several different pressures are
required within that range, the plant is usually
designed for the highest pressure. Typical low-
pressure systems include the following: air motors,
crane drives, starting motors for combustion engines,
shops, laundry and dry-cleaning plants, and general
service (tools, cleaning, painting, and soot blowing for
HTW generators and steam boilers).
Medium-pressure systems deliver air from 126 to
399 psig. Normally, this type of system provides an
individual compressor located near the load. Typical
applications are starting diesel engines, hydraulic lifts,
and retread tire molds.
High-pressure compressed air systems range from
400 to 6,000 psig. To minimize the hazard that exists
with higher pressures and capacities, you can use
separate compressors for each required pressure. Some
applications are torpedo workshop, ammunitions
depot, catapults, wind tunnel, and testing laboratories.
Distribution piping is either aboveground or
Both aboveground and underground
piping systems have advantages and disadvantages.
The advantages of each system are as follows:
Initial cost is lower
Less vulnerable target
Less obstruction to traffic
Easy detection of failure
Freeze protected when
Some other factors considered are permanent
versus temporary use, existence of high water table,
annual ownership, operation and maintenance costs,
and degree of hazard (example, potential danger that
overhead piping may cause to aircraft operations).
Low-pressure and medium-pressure systems use
black steel pipe.
Preferably the joints are welded.
Special conditions may require stainless steel and
copper tubing with appropriate fittings. Connections
to removable equipment are always flange fittings,
except when using small threaded pipe.
High-pressure systems use seamless steel pipe
with butt welded fittings. Screwed fittings, when used,
have their ends sealed by fillet welds and exposed pipe
threads covered with weld.
Piping supports are held in place by U-shaped or
similar types of hangers firmly secured to support
structures. Support hangers must fit closely around the
pipe, but may allow for slight movement.
Aboveground pipe is pitched downward a minimum of
3 inches per 100 feet of length, in the direction of the
airflow, to low points where the condensate is
collected and drained through drip legs. The drip legs
are at all low points, bottom of all risers, and every 200
to 300 feet from horizontally pitched pipe.