Quantcast Section 3. Operation of Steam Distribution Systems

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3.9.2  Waterproofing.  W a t e r t i g h t n e s s is an important requirement in manhole
Manholes are provided with an extra-heavy cast iron frame and a
construction.
w a t e r p r o o f cover, n o t less than 24 inches in diameter.  The bottom is
waterproofed by placement of a waterproof membrane between the concrete slab
and the earth, and the membrane is continued up the outer sides for at least
1 foot.  T h e exterior surface of the sides is coated with creosote primer and
c o a l t a r .  C o n d u i t seals are provided for all types of conduits at manholes
entrances.
3 . 9 . 3 Ladders.  A l l manholes 3-feet deep or more are furnished with side-rail
l a d d e r s fastened to the wall for safe and easy access. The ladder consists of
r o u n d steel rungs not less than 3/4-inch thick and uniformly spaced,
approximately 15 inches between centers.  T h e highest rung of the ladder is
g e n e r a l l y within 6 inches of the street surface.
In locations where the manhole bottom is above a nearby
3 . 9 . 4 Drainage.
sewer, the manhole can be drained by gravity to the sewer though a backwater
t r a p .  If no sewer is available or the manhole bottom is below the sewer,
water removing equipment is necessary.  A sump in the bottom of a manhole can
be drained by a motor operated pump or a steam ejector. The electrical
i n s t a l l a t i o n is heatproof and moistureproof.
4 CONDENSATE RETURN.  I n steam distribution systems that use ferrous
c o n d e n s a t e return lines, it is customary to provide a separate conduit for the
i n s u l a t e d condensate return piping.  T h i s is done because the return piping is
o f t e n subject to corrosion which makes its life considerably shorter than the
l i f e of the steam pipes.  When nonferrous condensate return lines are used,
t h e y are enclosed with the steam lines in the same conduit. In such cases,
the condensate return lines are insulated when required by economic
considerations.
5 PIPING.  S t e a m distribution systems generally use black steel pipe. The
c o n d e n s a t e return lines can be extra strong wrought iron, extra strong steel,
or copper.  J o i n t s for steel piping are usually welded, except those in
manholes, which may be flanged.  C o p p e r piping is provided with brazed
j o i n t s .  F o r information on valves, fittings, and associated equipment refer
t o chapter 7.
Section 3.
OPERATION OF STEAM DISTRIBUTION SYSTEMS
1 STARTUP INSPECTION.  B e f o r e placing a new steam distribution system in
s e r v i c e , or after a major overhaul to an existing system, check the following
i terns.
( a ) Make sure the system meets requirements set forth in the
specifications.
(b) See that applicable tests, as described in NAVFAC TR-733,
Heat-Traced System for Polar Regions (Latest Revision), have been
s a t i s f a c t o r i l y  completed.
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