3.8.2 Relief valves. Regulation of the pneumatic system pressure downstream
of the compressor pump shall be provided by a relief valve set to unseat at a
pressure between 3,700 psig and 3,900 psig, and to reseat at a pressure not less
than 3,500 psig. Additional relief valves shall be provided to individually
protect the moisture separator, the air receiver, and each stage of the
compressor pump, except that the last stage may be protected by a rupture disk.
In addition to the relief valves, rupture disks shall be provided to protect the
moisture separator and the air receiver. All relief valves shall be spring
loaded, adjustable, preset, and securely locked and sealed to prevent
unauthorized adjustment. Each relief valve and rupture disk shall be capable of
venting full delivery capacity.
3.8.3 Moisture separator. A mechanical-type moisture separator shall be
provided downstream of the aftercooler to remove condensed moisture and oil. The
separator shall be designed for a minimum operating pressure of 3,500 psig and a
proof pressure of 5,250 psig and shall be of a corrosion-resistant material. The
separator shall be large enough to contain the moisture and oil which would
accumulate in 20 minutes while the compressor is operating at rated capacity with
a relative humidity of not less than 85 percent and an ambient temperature of
120" F. A valve operated from the control panel shall be provided for periodic
drainage of the moisture separator. Periodic drainage shall not be required more
frequently than 15 minute intervals under all conditions specified herein. In
addition, automatic drainage of the moisture separator shall occur on shutdown of
the compressor. Provision shall be made to heat the moisture separator when
operating at ambient temperature below 40 F to prevent freezing of condensed
moisture, When an electric heater is utilized, it shall be designed for 28-volt
d.c. electric service and the outlet for the service line shall be located on the
control panel and shall mate with a plug conforming to MS3106A145-7S, with
voltage applied across the A and B contacts.
3.8.4 Dehydrator. A chemical-type dehydrator shall be provided and shall be
of the replaceable cartridge type, conforming to MIL-C-83959 and provided with an
MA-2 cartridge conforming-- to MIL-C-26058. The cylinder shall be rigidly mounted
in an accessible location and in any position from the vertical to 30 degrees
from the vertical measured when the compressor is in a normal level position.
Instructions for changing the cartridge in the cylinder shall be provided on an
instruction plate (see 3.16). Instructions shall also include the required hours
between cartridge changes for not less than three temperature ranges to maintain
a delivery air dewpoint of minus 65 F as determined during testing. Inter-
polation and extrapolation of test results will be permitted. A blank space
shall be provided on the instruction plate on which the hourmeter reading can be
recorded. A line filter with a replaceable element rated at not greater than 10
microns shall be installed downstream of the dehydrator.
3.8.5 Back pressure valve. A back pressure valve shall be provided to
maintain sufficient pressure to ensure the correct operation of the moisture
separator and dehydrator.
3.8.6 Check valve. The pnematic system shall be equipped with a check valve
to prevent reverse air flow from the receiver into upstream components.