Chemical Storage and Feeding Systems - Public Water Systems - page 842

the hopper and the fixed tray, which may be raised or lowered. This type of feeder is
one of the most widely used in small water plants.

Oscillating Plate Feeder. In the oscillating plate feeder, a plate is mounted below the
bottom spout in the storage hopper so that the chemical spills out onto the plate as it
comes out of the storage hopper. A leveling bar is mounted above the plate on each
of the two ends. The plate is mechanically linked to the drive motor and slowly
oscillates from side to side as the feeder operates. The magnitude of oscillation can
be adjusted with the mechanical linkage. This provides a dosage adjustment. Each
time the plate oscillates from one side to the other, a measured amount of chemical
drops off it into the solution tank. The rake bar above each end of the plate helps to
regulate the repeatability of the feed rate.

Vibrating Feeder. The vibrating feeder is also a volumetric feeder. With it, motion is
obtained by means of an electromagnet anchored to the feeding trough, which in turn
is mounted on flexible leaf springs. The magnet, energized by pulsating current, pulls
the trough sharply down and back; then the leaf springs return it up and forward to
its original position. This action is repeated 3,600 times per minute (when operating
on 60-cycle AC), producing a smooth, steady flow of material.

Volumetric Belt Feeder. The volumetric belt feeder uses a continuous belt of specific
width moving from under the hopper to the dissolving tank. The material falls on the
feed belt from the hopper and passes beneath a vertical gate. For a given belt speed,
the position of the gate determines the volume of material passing through the feeder.
A volumetric belt feeder is illustrated in Figure 24-11.

Screw-Type Feeder. The volumetric screw-type feeder employs a screw or helix at
the bottom of the hopper to transfer dry chemical to the solution chamber, as illustrated
in Figure 24-12 and pictured in Figures 24-12a and 24-12b.
The basic drawback of the volumetric feeder is that it cannot compensate for
changes in the density of materials and, therefore, is not as accurate as two other types
of dry feeders: the gravimetric and loss-in-weight types. For these feeders, the volu-
metric design is modified to include a gravimetric or loss-in-weight controller, which

FEED
BELT

FEED SECTION

GATE

STATIO NARY
DECK

Fig. 24-11. Volumetric belt-type feeder ( Source: Reference 7)