TM 5-4610-223-12
(b)
Raw water is continuously added through the raw water by-pass line. A portion of this water
flows through a constant head fixed orifice into the limestone slurry compartment and the remainder overflows to a weir
for dilution of the slurry discharge from the feeder. This diluted slurry flows by gravity into the downcomer.
(c)
The limestone slurry is kept in suspension by agitators within the limestone slurry compartment.
(d)
The feeder operates on a dilution principle whereby 65% of the initial charge of slurry is fed
during a l-hour period, therefore, the feeder requires recharging with dry chemical every hour. The limestone
compartment remains full of liquid slurry but becomes more diluted during the hour until recharged with the dry
chemicals.
WARNING
Do not pressurize the filter section without first ensuring that the filter housing clamp assembly and gasket
are properly seated and tightened.
b.
Filter Process. The filtering process further reduces suspended matter by use of diatomaceous earth filter
aid. The filtering process consists of three steps; precoating, filtering, and backwashing.
(1)
Precoatlng.
(a)
Before the water can be filtered, it is necessary to precoat the filter elements with diatomaceous
earth.
(b)
Diatomaceous earth slurry is added to the water line through the precoat funnels ( 16, fig. 1-3)
and valve CV-38 (1, fig. 2-23).
(c)
The water is pumped from the wet well tank through valves CV-34, SCV-35, and CV-36, which
are in FILTER position, and up into influent section (4, fig. 2-28) of the filters. The water rises until it starts escaping
through valve CV38 (1, fig. 2-23), which must now be closed.
(d)
Air is trapped and compressed In each plastic cup (7, fig. 2-28) of the filter elements (2) and in
the dome of the filter housing cover (1). The air is prevented from escaping through the air release valve ARV-50 (2, fig.
2-23) since it is closed in FILTER position.
(e)
As the water is filtered through the element membranes the diatomaceous earth and suspended
matter are deposited on the elements and the water enters the effluent section (5, fig. 2-28) through the two pipes from
each element.
2-50 Change 6
