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
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
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
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.
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
( a ) Make sure the system meets requirements set forth in the
(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.