MIL-HDBK-1005/16
1/2 inch per foot (2 to 4 cm/m) to facilitate drainage and
cleanup. For pumps too large to be lifted manually, a chain
hoist attachment, monorail, or traveling bridge crane sized to
handle the largest piece of equipment should be provided.
Hatches, doors, or removable walls should be provided where
appropriate to allow removal of equipment.
For primary solids pumping systems, provide surge
chambers with pressure gauges and flexible pump-to-piping
couplings on both the suction and discharge side of the pump.
A high-discharge pressure alarm and high-pressure shutdown system
should be provided. Seal water, where required, should be
potable water or filtered final effluent. Backflow preventers
are required if potable water is used.
Requirements concerning pump capacity, need for
duplicate units, minimum head, and sampling valves are given in
Ten State Standards (Great Lakes, 1990).
10.6
Solids Grinding. In-line solids grinders, which cut
large materials into small particles, are recommended upstream of
progressing cavity pumps and centrifuges to prevent clogging.
They are also beneficial upstream of belt filter presses to help
reduce belt damage and wear. Several manufacturers market
grinders, which have different maintenance requirements and
produce varying degrees of pulverized solids. Descriptions of
solids grinders and design information are provided in WEF MOP 8.
10.7
Solids Screening. Solids screening may be necessary to
ensure a uniform and visually acceptable product, to assist in
the operation of mechanical dewatering units, or to prevent
accumulation of rags and plastics in digesters. Solids screening
is more effective than grinding but also more costly and
maintenance-intensive. The solids screenings volume is estimated
at 10 to 75 cubic yards per day per million gallons (2 to
15 cubic meters per day per million liters) of plant influent.
Internal feed rotary screens are the recommended choice
for solids screening because of the cross-flow feed pattern,
which minimizes aligning of fibers with the openings and reduces
plugging problems. Static screens are not recommended for this
application because of clogging problems.
Screens should be sized to handle the maximum projected
solids stream flow, considering equalization available in the
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