MIL-HDBK-1005/16
flow whenever the pump operates are often used. These must be
manually adjusted whenever the pump stroke length is changed.
10.4.4
Diaphragm Pump. A diaphragm pump is a positive
displacement pump that delivers a volume equal to the
displacement of the driving element, a flexible diaphragm, on
each stroke. While several types of diaphragm pumps are
available, only the air-operated type with spring assist is
recommended for pumping primary solids. This type of pump is
suited to pumping thick solids (above 2 percent) but is not
recommended for pumping primary scum.
The air-operated diaphragm pump requires very clean,
high-pressure (80 to 124 psi [552 to 855 kPa]), low humidity
(-40oF [-40oC] dew point) air for operation. The air should be
delivered through a 1-1/4- to 1-1/2-inch (3 to 4 cm) minimum
supply tap. A timer-operated solenoid valve allows air to
rapidly enter and exit the pump operating chamber, which in turn
rapidly flexes the diaphragm. This results in high flow
velocities in both the suction and discharge piping, minimizing
pipe clogging problems but causing substantial surges that
require special consideration during design. For example, a
4-inch (10 cm) pump delivers a 3.8-gallon (14-L) stroke, which is
equivalent to about 250 gpm (16 L/s).
Because of the large forces on the pipeline, the design
must include adequate pipe restraints and flexible couplings
between the pump and piping. Air surge chambers and double ball
checks should be provided on both the suction and discharge sides
to protect the piping. A muffler is required on the air
discharge.
10.4.5
Rotary Lobe Pump. Rotary lobe pumps use synchronized
cams inside a chamber. Voids between the cams and the chamber
fill with the material being pumped and force it from the suction
side to the discharge side. Because of the close tolerance and
lack of natural flushing between the lobes and the chamber
housing, there have been extensive problems in the past with
excessive wear when pumping abrasive materials. As a result,
these pumps may be applicable for scum pumping but not for
pumping of other wastewater solids streams.
10.5
Pumping System Design. Arrange pumps so that they can
be easily serviced, with adequate space and lighting. The floor
where the pumps are located should generally be sloped 1/4 to
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