MIL-HDBK 1028/6A
Section 6:
UNDERGROUND INSTALLATIONS
6.1
Mains and Feeders. Fixed point-utility services shall be
distributed to the hangar and parking apron in underground mains. The
mains shall be installed in the same trench with access at the transition
gate boxes. The routing of mains between the central facilities and the
gate boxes shall be outside the apron and taxiway concrete as much as
possible. Underground installation, including distribution box designs,
shall conform to the requirements of NAVFAC DM-21.3, Flexible Pavement
Design for Airfields and MIL-HDBK-1021/4, Rigid Pavement Design for
Airfields.
6.1.1
Compressed Air Piping. Underground compressed air piping shall
be carbon steel welded construction with a polyethylene coating. Pipe
shall be laid on a 6 in. (152 mm) sand base with granular backfill.
Horizontal and vertical alignment shall be maintained. Entrances to
service islands shall be through sleeves with link seals. Underground
piping shall have cathodic protection. The underground compressed air
distribution piping should be arranged with loops to equalize distribution
line pressure throughout. Depending on the system layout, sectionalizing
valves may be provided for maintenance purposes.
6.1.2
Electrical. Electrical conduit shall be nonmetallic
installed in concrete encased duct banks in accordance with NFGS-16302.
6.2
Service Access Points. Access to compressed air line valving
shall be provided through flush-mounted valve boxes, valving shall provide
isolation for line segments as indicated in Figure 1. Electrical feeders
shall be terminated in feeder distribution centers and service point
enclosures.
6.2.1
Valve Boxes. Compressed air shutoff valves on underground main
loop and branch piping shall be installed in valve boxes flush with grade,
with flush mounted removable cast-iron covers.
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