Chemical Storage and Feeding Systems - Public Water Systems - page 840

by the bagful into a dissolving tank. This method is generally limited to very small
operations, however, and dry chemical feed equipment is required in larger installa-
tions.
A dry feed installation is shown schematically in Figure 24-9, and consists of a
storage bin and / or hopper, a feeder, and a dissolver tank. Dry feeders are either of the
volumetric of the gravimetric type. Volumetric feeders usually are used only where
low feed rates are required. These feeders deliver a constant, preset amount of chemical
and do not recognize changes in material density. This type of feeder must be cali-
brated by trial and error at the outset, and then readjusted periodically if the material
changes in density.
The gravimetric feeder delivers chemicals based on the required weight per unit
volume. Typically, the volumetric feeders are less expensive than the gravimetric units.
Most types of volumetric feeders generally fall into the positive displacement cat-
egory. All designs of this type use some form of moving cavity of a specific or variable

DUST COLLECTOR

FILL PIPE (PNEUMATIC)

DUST COLLECTOR

BULK STORAGE
BIN

BAG FILL

DAY HOPPER
FOR DRY CHEMICAL
FROM BAGS OR DRUMS

SCREEN
WITH BREAKER

BIN GATE

FLEXIBLE
CONNECTION

ALTERNATE SUPPLIES DEPENDING
ON STORAGE

DUST AND VAPOR REMOVE R
WATER
SUPPLY

SCALE OR SAMPLE CHUTE

FEEDER

DRAIN
SOLENOID V ALVE

MIXER

BAFFLE

CONTROL
VA LVE

ROTAMETER

DISSOLVER

PRESSURE REDU CING
VA LVE

GRAVITY TO
APPLICATION

LEVEL
PROBES

WATER SUPPLY

HOLDING
TANK

PUMP
TO APPLICATION

Fig. 24-9. Typical solid or dry chemical feed system (From Culp, Gordon, and Williams, Robert,
Handbook of Public Water Systems. Copyright 1986 by John Wiley & Sons, Inc. Reprinted by
permission of John Wiley & Sons, Inc.)