UFC 4-390-01
23 July 2003
Unmanned pressure vessels are of two types, those pressurized
using a gas and those pressurized using fluid. Because of the
differences in the pressurizing medium, selection of components
of the different systems should be given different
considerations.
B.8.2.1 Components of Gas Pressurized Systems. Only seamless
piping or tubing is authorized in DOD unmanned pressure test
facilities.
B.8.2.1.1 Compressors.
Required features include pressure
gages for each stage of compression, running hour meter, high-
pressure shutdown, high temperature shutdown/alarm and low oil
pressure shutdown/alarm. It is recommended that automatic
condensate drains be installed on compressors. Consideration must
be given to the location of the compressor inlet in regards to
possible contamination from machinery exhaust fumes or other
airborne contaminants. Proper inlet filtration should be
provided. A dry type, non-shedding inlet filter is recommended.
B.8.2.1.1.1 Coolers. High temperatures associated with high-
pressure air compressors may cause compressor lubricants to break
down. Therefore, compressor inter-stage coolers and after
coolers may be required to bring the discharge temperatures down
to an acceptable level.
B.8.2.1.2 Moisture Separators. All high-pressure air
compressors require moisture separators to remove liquid
contaminants from the compressed air. The moisture separator
capacity is selected according to compressor output flow rate and
temperature and the anticipated environment that the compressor
will be used in.
Separators should be located downstream of any after coolers to
trap the condensation resulting from the air cooling process and
compressor oil which may enter the outlet gas stream. All
separators must be provided with drain valves to remove collected
liquid. For maximum efficiency, moisture separators should be
installed in a straight length of pipe at least 10 pipe diameters
downstream of the nearest valve or fitting and should be drained
regularly during operation. All moisture separators should be
visually and hydrostatically tested. The periodicity for
hydrostatically testing the moisture should be negotiated with
the SCA.
B.8.2.1.3 Back Pressure Regulators. High-pressure air
compressors should be equipped with a backpressure regulator
located downstream of the moisture separator. Backpressure
regulators should be designed to maintain a specified minimum
operating pressure (normally 1000 psig or greater in accordance
with the compressor manufacturer's requirements) at the
compressor outlet. The backpressure regulator is used to seat
the compressor piston rings and prevent excessive compressor
lubricating oil from entering the system piping.
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