ride. Mixture of these two chemicals
will produce chlorine gas (greenish-
(a) When the air release valve ARV-49 is in
yellow in color) which is an extreme
the BACKWASH position, some of the air com-
irritant to the throat and lungs. It will
pressed in the dome of the filter housing cover by-
cause coughing, difficult breathing
passes the main air valve. This air depresses a di-
and, in sufficient concentration, can
aphragm in the top of the main valve and opens a
lead to DEATH.
valve releasing the air in the dome to the atmo-
sphere. This sudden release of air allows the air
a. Preparation for Starting.
compressed in the cups (fig. 2-5) in each element to
(1) Perform the before-operation services,
expand and force water back through the element
filter cakes. This rapid reversal of the water usually
(2) Lubricate the water purification unit as
dislodges all the suspended matter form the ele-
specified in the current lubrication order.
ments. If it does not, the elements must be removed
b. Water Quality Analysis Testing. In order
to set the proper feed rates it is essential that the
(b) Most of the removed suspended matter
quality of the raw water to be treated be known. To
and the water in the influent section will drain to
determine the raw water quality, the operator
waste through the filter drain valve DV-48 (fig. 2-
should use the Water Quality Analysis Set, NSN
1). However, some of the suspended matter will set-
tle on the conical bottom of the influent pipe and
form various chemical analysis on the water to be
must be washed away. When valve CV-36 is in the
treated and gives guidance on proper feed rates. The
WASH position, it allows the water to enter the
supporting manual for the Analysis Set is TM 5-
wash ring (fig. 2-5) and wash the sediment from the
6630-215-12, Water Quality Analysis Sets, Pre-
bottom of the filter, After washing, the filter is
ventive Medicine, NSN 6630-00-140-7826, and En-
ready for precoating.
c. Preparation of Ferric Chloride Solution.
2-8. Starting Water Treatment Section.
(1) Initial base charge. The initial base
charge for ferric chloride solution as shown on the
ferric chloride solution scale reading (fig. 2-6) is one
Use extreme caution to avoid mixing
pound of ferric chloride per two gallons of raw
calcium hypochlorite and ferric chlo-
Figure 2-6. Ferric chloride solution calibration chart.