10 January 2002
provides construction details for this cover. The concrete cover detailed is designed for loadings up to 150 psf.
For greater loadings, the design must be re-evaluated. A disadvantage of concrete covers is the difficulty in
providing ventilation. For concrete shallow trench systems, a single 6 inch gooseneck pipe will be used, as
detailed in figure 3-21, to allow steam to exit the valve manhole if a leak or excessive heat loss is present.
Note that for shallow trench systems, the gooseneck will be installed off to one side of the valve manhole
concrete top to minimize pedestrian traffic interference. For Pre-engineered Underground Heat Distribution
Systems, two 6 inch goosenecks will be used. One will extend below the top as detailed in figure 3-21. The
other will be similar but will extend to within 8 inches of the valve manhole floor on the opposite side of the
d. Valve manhole drainage. Drainage of water from the valve manhole is mandatory for the successful
operation and longevity of buried heating or cooling distribution systems. There are three types of valve
manhole drainage systems described in this manual: gravity drainage, pumped drainage from a sump basin,
and pumped drainage from the valve manhole.
(1) Gravity drainage. The most cost effective and lowest maintenance system is gravity drainage to
a storm drain when location, depth of existing storm drains, and local regulatory requirements allow this
possibility. Drainage lines will be 6 inches in diameter minimum and will conform to the latest storm drain
criteria and will be sloped at one percent, minimum. Valve manhole outlet will be a floor drain with backflow
preventer to prevent storm water inflow from the storm drain (see figure 3-22). Note that valve manhole drain
outlets shall be covered with a "hat type" cast iron pipe screen to minimize the accumulation of trash over the
drain inlet. Also, the manhole floor will be sloped toward the drain.
(2) Pumped drainage from sump basin. For pumped drainage, a duplex submersible pump system
installed in a remote sump basin may be provided as indicated in figures 3-23 and 3-24. The sump basin will
be located no more than 10 feet from the valve manhole. Drainage from the valve manhole to the sump basin
will be similar to drainage to a storm drain including the valve manhole floor drain (fig 3-22). Discharge from
the pumps can be routed to a splashblock at grade or to an adjacent storm sewer. Design of the surrounding
grade must ensure drainage away from the sump basin, valve manhole and concrete shallow trench (if used)
when discharging to grade. A power pedestal complete with failure warning light will be provided with each
basin as shown in figure 3-25. A typical wiring diagram and sequence of operation are shown in figure 3-26. A
specification for the sump basin system can be included in the applicable manhole or heat distribution section
of the contract specification. The sump basin design has proven to operate well even in the colder climates of
the upper tier states in the continental United States. It is also an excellent method to retrofit existing
manholes that currently do not drain properly. The remote sump basin increases the life of the systems by
removing the sump pump and pump controls from the hot, humid environment of the manhole. Also, pump
maintenance will be done outside of the manhole. The pumps are easily disconnected and lifted to grade.
The sump pumps used in the sump basin must incorporate the design characteristics listed in table 3-3.
(3) Pumped drainage from valve manhole. Another means to pump water from the manhole is to
locate the duplex sump pumps in the valve manhole. Typically, a 2'0" by 2'0" by 1'0" (deep) sump will be
provided in a corner of the valve manhole. The duplex sump pumps will be installed to pump
out of this sump. Valve manhole sump pump electrical arrangement should be installed as shown in figure
3-27. The control panel with high level warning light will be mounted adjacent to the valve manhole at grade.
This keeps the electrical panel out of the hot, humid environment of the manhole. The sequence of operation
and wiring diagrams will meet the requirements of figure 3-26. Pump discharge can be routed to a
splashblock at grade (similar to the sump basin discharge piping arrangement on figure 3-23) or to an adjacent
storm drain. Electric sump pumps used in the valve manholes must incorporate the design characteristics
listed in table 3-3. Note that life of the pumps are typically shortened when installed in the hot and humid
valve manhole environment.
(1) Valve manhole wall penetrations. A design mus t be provided for the distribution system wall