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(e) Drip Legs.  The low line points are provided with drip legs equipped
with scale pockets and automatic drain traps.  When accessible, scale pockets
may have a manual drain valve instead of an automatic drain trap.  Drip legs
are located at:
Low points
B o t t o m of all risers
Every 200 to 300 feet for horizontally pitched pipe
( f ) Counterflow of Condensate.  Where pipes must be sloped upward,
causing condensate to run in a direction opposite to airflow, the pitch of the
pipe is increased to a minimum of 6 inches per 100 feet.
5 UNDERGROUND DISTRIBUTION SYSTEM.  Selection of the route for an underground
d i s t r i b u t i o n system involves consideration and evaluation of the following
( a ) Walking Tunnel.  A concrete tunnel containing piping for
miscellaneous services may also be used to house compressed air pipes.
( b ) Trenches.  A concrete trench used for miscellaneous service pipes
may be designed to include air lines.
( c ) Manholes.  Access to underground conduit for inspection, repair, and
v e n t i l a t i o n of service piping is provided by manholes.
( d ) D i r e c t B u r i a l .  Direct burial is the method most commonly used for
c o m p r e s s e d air distribution lines.  Because this type of construction
g e n e r a l l y lowers the air temperature causing additional condensation, it is
i m p o r t a n t that the piping be properly pitched to collect condensation at drip
legs.  Drip legs can be located in building basements; however, manholes may
be required at low points of long distribution systems to house moisture
t r a p s .  Corrosion control by cathodic protection may be required depending on
soil corrosivity.
( e ) Pipe Covering.  Buried compressed air lines generally require no
However, they should be shop coated, wrapped: tested, and handled
in accordance with NAVFAC Specification 34Y (Latest Revision), Bituminous
Coating for Steel Surfaces.
(f) Pitch of Underground Systems.  A i r lines are generally pitched down
a minimum of 3 inches per 100 feet of length, in the direction of airflow, to
provide easy drainage of condensate.
( g ) Drip Legs.  R e f e r to section 2, paragraph 4(e). In horizontally
p i t c h e d buried pipes where traps are inaccessible, drip legs are located at
i n t e r v a l s of not over 500 feet.
(h) Counterflow of Condensate.
R e f e r to section 2, paragraph 4(f).
6 . 1 Piping Design.  W h e n practical, pipelines distributing compressed air to
numerous branches or service outlets in a large area should form a closed


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