The diffuser holder assembly shall be of the fixed type [or swing-out type].
a.
Fixed Type Diffuser Holder Assembly: The assembly shall include
an air control and shut-off valve and all air piping downstream
from this valve. Valve shall be of the butterfly valve, plug
valve, or globe valve type and be suitable for air control with
indicator markings for throttling and complete shut-off.
Butterfly valve shall conform to AWWA C504, and globe valve shall
conform to MSS SP-80, shall have cast-iron body and chloroprene
rubber seat, and shall be lever or handwheel operated. Spacing of
diffuser assemblies in the basin shall be such as to provide air
diffuser nozzles mounted approximately 150 mm 6 inches on centers.
The drop-pipes shall be provided with union or equivalent
connection adjacent to the air header to permit raising the
drop-pipe above the water surface readily. The drilling and
tapping of the horizontal portion of drop-pipes shall be such as
to give the diffuser correct horizontal alignment without being
skewed either upward or downward.
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NOTE: Delete the paragraph when steel plant only is
required. This specification is structured for
steel plant only, concrete plant only, or steel or
concrete plant at the Contractor's option. Among
the factors to be considered are initial cost,
maintenance costs, life expectancy, and possible
need for relocation during period of useful life.
Steel plant is generally more economical in first
cost than concrete plant; however, maintenance costs
may be higher. Concrete plant would have a higher
life expectancy in highly corrosive soils. Small
steel plants are suitable for relocation. Concrete
plant is considered as plant having outer walls of
concrete regardless of material used for interior
walls or partitions. Steel plants are considered as
plants having outer walls of steel and bottom of
steel or concrete (except that all-steel would be
needed for relocatable plants).
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b.
Swing-out Type Diffuser Holder Assembly: The assembly shall
include an upper pivot joint with air control and shut-off valve
and a drop-pipe with intermediate pivot joint, and a diffuser
header. The upper pivot joint shall be of cast iron or cast steel
and shall have a trunnion type support for the rotary joint. The
unit shall have a base flange for mounting to a wall anchorage
elbow, and the joint shall rotate on two bronze sleeve bearings
either permanently lubricated or with suitable grease fittings for
lubrication. Chloroprene or Buna N rubber O-ring gaskets shall be
included at each pivot bearing to insure air and water tightness.
Valve shall be butterfly type and be suitable for air control with
indicator markings for throttling and complete shut-off.
Butterfly valve shall conform to AWWA C504, shall have a cast-iron
or bronze body and chloroprene rubber seat, and shall be lever or
handwheel operated. Means shall be provided for shut-off of air
supply when diffuser holder assembly is in raised position. The
intermediate pivot joint shall be as specified for the upper
joint, except that it shall not have the integral valve and base
SECTION 11375N
Page 37
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