MIL-HDBK-1003/6
that one compressor is 100 percent loaded 50 percent of the time. The motor,
or other driver, shall be sized so that it cannot be overloaded. Provide
unloading devices and/or other controls to reduce power consumption.
b) Intercoolers are required for two stage compression. After-
coolers are required at discharge. A receiver with an automatic water trap
shall be provided after the aftercooler.
c) Air driers and oil-moisture separators are required on
instrument air to prevent malfunctions of instruments. An air drier should be
considered on plant air if there is a possibility of moisture freezing in the
lines and blocking the air flow. An oil-moisture separator shall be placed
upstream of each outlet or usage point.
d) Intake filter-silencer on each compressor inlet or intake.
Compressor inlet air should be taken from outside air. The intake should be
at least 6 ft (1.52 m) above the ground and adequately protected from the
rain. Do not locate the inlet in areas where air pressure pulsations may
occur. Intake pipe shall not be less than full size of compressor inlet and
possibly larger if excessive length of pipe gives unacceptable pressure drop.
e) Emergency cross connection with moisture-oil separator between
plant air and instrument air.
f) Temporary connections, hoses and screwed joints shall be
minimized to reduce possible leakage.
Leakage. Design at least 10 percent additional capacity into the
8.8.4
system for leakage. An empirical rule of thumb is that 25 horsepower is
required to compress 100 square feet (9.29 square meters) of air at standard
conditions to 100 psig (690 kPa). Air at standard conditions weighs 0.075
pounds per cubic foot (1.21 kg per cubic meter). Because of the high cost of
air leakage, shut-off valves shall be provided at branches to permit
maintenance shut-down of individual usages of compressed air.
A check on the amount of total leakage throughout system may be
done by observing what portion of the air compressor capacity is required to
maintain pressure when no air-consuming equipment is in service.
8.9
Steam Traps
8.9.1
Types. There are three major classifications of steam traps:
mechanical, thermostatic, and thermodynamic. Their functions can sometimes be
mixed to create a combination steam trap.
Mechanical. A mechanical steam trap operates using the density
8.9.1.1
difference of condensate and steam. Steam will travel above the condensate
flowing along the bottom of any container. An increase of condensate results
in a rise of the liquid level of condensate. As the level rises, a mechanism
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