*TM 5-810-4/AFM 88-8, Chap. 3
An economic evaluation is necessary to determine whether a
demands. In the automatic position. a time delay relay allows
central compressed air distribution system or a system of
the compressor to operate for a predetermined length of time
separate compressors located near the point of usage is most
unloaded, and then stops the unit. An air demand will again
cost-effective. Selection of the number of compressors for
start the unit, when needed. For multiple compressor sys-
either situation should be based upon economics and other
tems, the automatic start/stop sequence should alternate
factors such as system reliability. Seasonal or operational
among all compressors.
load variations must also be considered. The efficiency of
larger compressors is generally higher than that of smaller
3-11. Sound tests.
units, but use of smaller air-cooled units permits savings on
After installation, a sound test must be performed on all
water, water piping, and system losses. Multiple units with
compressors and accessories. Sound reading test results must
not exceed limitations set by OSHA Standard 1910.95. Mea-
interconnecting piping give flexibility for maintenance shut-
down of one compressor. A smaller air compressor to handle
surement of sound emitted from installed and operating air
requirements for weekends, holidays, and other low usage
compressors will be in accordance with CAGI Compressed
times may also be economical.
Air and Gas Handbook, Appendix B, "CAGI Pneurop Test
Code for the Measurement of Sound from Pneumatic Equip-
Compressors are to be located in clean, well lighted, and
ventilated areas of sufficient size to permit easy access for
cleaning, inspection, and any necessary dismantling, such as
removal of pistons, wheels, crankshafts, intercoolers, motors,
and drivers. Adequate aisle space is needed between items of
equipment for normal maintenance as well as for equipment
removal and replacement.
Automatic warning and shutdown.
Air compressor systems will be protected against high tem-
perature, high pressure, low oil pressure, and in the case of
centrifugal compressors, excessive vibration. Protective
controls will include a fault indicator and a manual reset
3-8. Vibration limits.
Compressor manufacturers should be contacted to obtain
guidance for establishing representative centrifugal com-
pressor vibration levels.
3-9. Lubrication system.
System design will be in accordance with the manufacturer*s
recommendations. Lubricant type will depend on the com-
a. Gravity, splash, or pressure petroleum oil will be used
use is not a problem.
b. Synthetic liquid lubricants will be used where there is
a danger of fire, where the carbonaceous deposits must be
reduced, or where lubricant is provided for extended mainte-
c. Solid lubricants, such as carbon or Teflon piston
rings, will be used for oil-free reciprocating compressed air
3-10. Control systems.
Energy can be conserved with a combination of pneumatic
cylinder unloading and a manual-off-automatic selector
switch on the compressor. When in the manual position, the
compressor loads and unloads to meet compressed air