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Q: Can an air dryer really make much of a difference?
A: Hot air holds more water. Every 20° F increase in temperature
doubles the amount of moisture suspended in air. Every 20°
F decrease in temperature reduces the amount of moisture suspended
in air in half. An aftercooler or air dryer can eliminate this
fluctuation. Air entering a 10hp compressor at 75° F and 75
percent relative humidity would produce 6.3 gallons of water per
day. An air-cooled aftercooler with a separator would remove 4.3
gallons per day and a refrigerated air dryer would remove an additional
1.7 gallons. Only .3 gallons would be left within the 50,400 cubic
foot of compressed air.
Q: How much water is generated by my air system?
A: One 100 cfm compressor operating at 100 psig will generate
18 gallons per day at 90° F and 50 percent RH. About 60 percent
of this moisture will be removed by the aftercooler. The remainder
will pass into your compressed air system if a dryer is not installed.
Q: Which filters and dryers do I need for my application
in order to eliminate moisture and contaminants in my airlines?
A: This depends on the application and required dewpoint. For
most applications, a 35° F dewpoint is sufficient, which can
be provided by a refrigerated air dryer. For outdoor applications,
a desiccant dryer will be necessary to provide a -40° F dewpoint.
Filters will provide various levels of contaminant removal and
can be selected according to the application requirements.
Q: How many cubic feet does a receiver hold?
A: Only stored air above the pressure being used is defined as
useful free air. Majority of pneumatic tools and work processes
only require 90 to 100 spi. Storing compressed air above this
working pressure provides a surplus of useful air that can accommodate
work demands. A 120-gallon receiver at 175 psi stored provides
193 cubic feet of compressed air.
Q: What size piping is needed in a properly designed system
to minimize pressure drop?
A: This would depend on the capacity (CFM) of your air compressors,
the required pressure and the total length of piping in the system.
By knowing those three factors, standard tables can be used to
determine the size of pipe required to minimize pressure drop.
It is also important to know the number of valves and elbows in
the system, as each one counts as an equivalent length of straight
pipe. Size piping for the maximum CFM required and include the
current system capacity and possible future expansion in your
piping plan.
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