10 January 2002
(5) Isolation flanges. Isolation flanges will be provided when connecting to an existing cathodically
protected heating or cooling distribution system or to prevent a new system's cathodic protection system
from contacting an existing system. The isolation flanges will be installed in the valve manhole and a typical
flange detail is shown in figure 3-3.
(6) Valve/piping supports. Piping in valve manholes often will need supports within the manhole
especially when larger valves or equipment are attached to the piping. These supports will be located on the
manhole plans as determined by the designer's expansion compensation calculations for each manhole
valving and equipment layout. Typical valve/piping support details are shown in figure 3-4.
b. Valve manhole construction. Valve manholes will be field constructed of reinforced concrete
conforming to the current criteria. Valve manholes will be constructed of 4,000 psi minimum compressive
strength concrete. Reinforcing bars will conform to ASTM A 615, grade 60. Typical reinforcing steel details
and sizing are shown in figure 3-5 and table 3-2 respectively. Concrete floor slabs and walls will be of
sufficient weight to prevent flotation in high water table areas. Floor slabs will be sloped to the drain which will
be installed in the floor slab. Concrete wall sections will be not less than 8 inches thick and must meet
anticipated load and soil conditions. Side walls will be constructed in a monolithic pour. Water stops will be
provided at all construction joints. Do not locate valve manholes in roads or parking areas which create an
inadequate amount of manhole ventilation and poor access.
c. Valve manhole covers. The valve manhole cover types discussed here are: raised solid plate,
supported cover, and concrete.
(1) Raised solid plate covers. Raised solid plate covers are preferred for HTHW and
steam/condensate systems installed in Pre-Engineered Underground Heat Distribution Systems. For shallow
concrete trench systems, the raised solid plate cover's raised feature will int erfere with the trench's walkway
function. When the valve manhole cover must remain flush with the trench top, the supported cover is the
preferred type. For the raised solid plate cover, ventilation openings are provided around the entire perimeter
below the raised top. The height of the valve manhole wall above grade (6 inches, minimum) shall be sufficient
to prevent surface water entry. The solid plate cover assembly is removable. The cover, constructed of
aluminum, also provides sectionalized access for inspection and maintenance. The solid plate cover raised
frame design and section, lifting lug, and handle details are shown in figure 3-6 through 3-12. Figure 3-13
contains notes for raised solid plate cover figures.
(2) Supported covers. Supported covers may be used for any distribution system covered in this
manual. For Pre-engineered Underground or Prefabricated Underground Heat Distribution Systems, design
the cover to be at least 6 inches above the surrounding grade. When used for concrete shallow trench
systems, the finished top will be flush with the concrete trench top. Required grates or other structural
members used for supporting covers to be made of corrosion resistant material such as aluminum or
galvanized steel. Details for the supporting cover are shown in figures 3-14 through 3-18. These details are
designed for loadings up to 150 psf and must be re-evaluated for larger loadings. Other structural solutions for
supporting the checkered plate are acceptable. The checkered plate cover (also referred to as diamond or
embossed plate) as shown in figure 3-18, will be installed over grating or other structural supports in most
locations to minimize the influx of leaves and other debris. The checkered plate is attached to the grating and
(3) Concrete covers. The use of concrete covers is discouraged, but, if used, they must be used with
4 x 4 ft. aluminum doors for any distribution system covered in this manual. Concrete covers should only be
used if desired by the user or if specific design conditions exist, such as below to aboveground system
transitions. When used for Pre-engineered Underground or Prefabricated Underground Heat Distribution
Systems, design the top of the concrete cover to be a minimum of 6 inches above the surrounding grade.
When used for concrete shallow trenches, design the cover to be flush with the trench top. Concrete
requirements for this cover are similar to those required for valve manhole construction. Concrete cover will be
designed to support anticipated loadings. Figure 3-19 shows a typical concrete cover plan and figure 3-20