c. Backwashing. The fiIter elements must be backwashed and the fiIter tank
drained whenever the fiIter elements become so clogged as to interfere with normal
operation. This condition is indicated whenever the flow through the fiIter stops or when
the effluent pressure gauge (see figure 5-11, circle E) reading drops to 5 pounds per
square inch (psi). (Normal operating pressure is approximately 30 psi.) To backwash
the fiIter, the effluent control valve (see figure 5-11, circle F) is closed; the fiIter pump is
operated untiI the influent pressure gauge (see figure 5-11, circle G) reads the same as
the fiIter effluent gauge (see figure 5-11, circle E). The pump is then stopped and the
influent control valve (see figure 5-11, circle H) is closed. Then the air release valve
(see figure 5-11, circle I) is opened (BACKWASH position), releasing the air
compressed in the filter dome (see figure 5-11, circle J) and in the plastic cups within
the fiIter elements, thus forcing water in a reverse direction through the fiIter cake. This
sudden reversal of water usually dislodges all the fiIter cake and foreign material. If it
does not, the elements must be disassembled and cleaned. After backwashing, the
fiIter drain (see figure 5-11, circle K) and the influent control valve (see figure 5-11.
circle H) are opened and the pump is operated for at least one minute to flush the fiIter.
Backwash water should never be drained into a soakage pit or returned to the
The electrical controls for operating the WPU are on the door of the electrical
control cabinet (see figure 5-12), which is located just forward of the erdlator assembly.
The electrical controls are as follows:
a. The low level warning Iight, located above the control cabinet (see
figure 5-12, circle A), turns on automatically when the water in the erdlator wet well tank
falls below a preset level. It is a red Iight, which is accompanied by a buzzer to provide
an audio warning. A toggle switch (see figure 5-12, circle B), located on the left side of
the door, is provided to turn off the warning Iight and buzzer.
circle D) are provided to indicate the current and voltage outputs, respectively, of the
c. Six start-stop button switches (see figure 5-12. circle E) are used to start and
stop the slurry feeders, filter pump, erdlator agitator, distribution pump, raw water pump,
and solution feeders.
The operations described in paragraphs 5-4 through 5-9, above, are intended
as a brief familiarization with the operation of the WPU and NOT as a
substitute for the detailed instructions contained in the TM pertaining to the
particular item of equipment in use.