Legend for figure 2-28:
1. Filter housing cover
2. Filter element (6 reqd)
3. Filter window
Plastic cups (84 reqd)
4. Influent section
The water then goes through valves CV-40 (11, fig. 2-23), CV-45 (6), and tV-46 (5), which are in the
RECIRCULATION position, and back to the wet well tank. The water is recirculated through the filter until it appears
clear when viewed through the filter window.
Filtering removes the remaining suspended matter and organisms from the water.
The flow of water from the wet well and through the filter is the same as during precoating, until it
reaches valve CV-46 (5, fig. 2-23) which is now in FILTER position to allow the water to flow through the filter water hose
to the storage tanks.
Diatomite slurry is discharged from the diatomite slurry compartment of the chemical slurry feeder
(1, fig. 2-10) to the water line on the suction side of the filter pump.
The flow of water carries the diatomite slurry to the filter where it is deposited on the filter elements.
The continuous feed of diatomite slurry maintains the porosity of the filter cake and permits longer filter runs. As water is
pumped through the diatomite filter cake, suspended matter in the water will gradually plug the filter cake and increase
the pressure differential across the filter elements. When the effluent pressure gage PG-3 (8, fig. 2-23) indicates a
pressure of 5 psi, the filter is ready to be backwashed. The filter cycle is the time the filter is in operation, from the time
precoat has been added until the filter elements must be backwashed.
When air release valve CV-36 (3, fig. 2-17) is in BACKWASH position some air compressed in the
dome of the filter housing cover bypasses the main air valve. This air depresses a diaphragm in the top of the main
valve and opens a valve releasing air in the dome to the atmosphere. This sudden release of air allows the air
compressed in the cups (7, fig. 2-28) in each element (2) to expand and force water back through the element filter
cakes. This rapid reversal of the water usually dislodges all the suspended matter from the elements. If it does not, the
elements must be removed and cleaned.
Most of the removed suspended matter and the water in the influent section will drain to waste
through the filter drain valve DV-49 (16, fig. 2-23). However, some of the suspended matter will settle on the conical
bottom of the influent pipe and must be