the compartment floor. Water from the water (heater
as water is removed from the water tank.
(5) Level indicator. By measuring the difference
pressure relief) valve will flow out of the floor drain
manifold. The floor drain manifold may be lifted slightly,
between the air at the top of the water tank and the water
if required, to allow the water on the compartment floor to
at the bottom, the level indicator monitors the level of
drain to the outside of the darkroom.
water in the water tank.
f. Water System Indicators. The functions of the
2-10. Silver Recovery Unit
indicators used to monitor the operation of the water
a. The silver recovery unit removes silver from the
system are described below.
photographic fixer solution by the electrolytic method.
(1) Inlet pressure indicator. The inlet pressure
Power is applied to the unit through LOW OFF HIGH
indicator measures the pressure of the water as it leaves
switch S1 (fig. 23). When power is applied, the cathode
the pressure regulator. If the pressure regulator is
is positively charged and the anodes (fig. 24) are
functioning normally, the maximum pressure indicated
negatively charged. The silver particles in the fixer
will be 40 psi.
solution become negatively charged. The silver particles
(2) Outlet pressure indicator. The outlet pressure
are then attracted to the positively charged cathode to
indicator measures the actual water pressure in the
which they adhere. The cathode is rotated by the motor
system. A difference in pressure between the outlet and
and fan assembly through the gears.
inlet pressure indicators is caused by obstruction to the
waterflow due to the accumulation of foreign particles in
b. The LOW OFF HIGH switch (fig. 23) applies
the 2micron filter.
power to the cathode and motor and fan assembly M1.
(3) Flow indicator. Any flow of water within the water
The power applied to the motor and fan assembly does
system will cause the white needle within the flow to
not vary, whether switch S1 is in the LOW or HIGH
indicator to spin, indicating both waterflow direction of
position. Therefore, the rotational speed of the cathode
is constant when the unit is operating. When the position
(4) Pressure vacuum indicator. When valve S8 is
of switch S1 is changed to HIGH or LOW, only the power
closed, the pressure vacuum indicator will indicate the
applied to the cathode is changed, to apply either low or
amount of vacuum at the top of the water tank in psi,
high plating current.
Change 2 1-2