onto the film and back to the sump. Both systems are in common use. Each has
its advantages and disadvantages. When spray processing, the oxidation process
is speeded up, since the exposure of developer to air is accelerated. This is
why some systems use the developer only once, after which it is drained.
(2) In systems where the solution is used again, the machine is equipped
with a replenishment system to offset the effects of oxidation.
In either
system, it helps to use a developer formula with a high preservation content.
There are some complex systems in which the air within the machine developing
tank is evacuated and replaced with nitrogen gas.
Nitrogen gas does not
support oxidation, and developer used in a nitrogen environment may be
recovered and used again and again.
d. Spray-immersion.
This is a third agitation system and as the name
implies, a combination of the preceding two. In a spray-immersion system the
spray bars are submerged in the solution so that the film receives agitation
from both the spray action and immersion in the solution.
e. Gaseous Burst. Another method is called the gaseous burst system. In
this system a photographically inert gas (nitrogen) is bubbled through the
solution from a perforated grill in the bottom of the tank at short intervals.
The gas bubbles rising through the solution keep it in motion to bring fresh
solution into contact with the film.
Another method is called turbulation.
This is a system where the solution is pumped out of the tank, usually near the
top, and back into the tank, usually near the bottom. Keeping the solution in
motion again provides fresh solution to the film surface. Many processors use
several of these agitation methods at the same time.
f. There are advantages and disadvantages to each major chemical system.
The spray concept gives excellent rapid processing. However, adjustment of the
spray fan to minimize streaking is critical.
In the spray processor, the
cabinet doors may be opened making all cabinet areas accessible for cleaning.
Since solutions do not remain in the cabinets, there is no drastic buildup of
chemical byproducts in the machine. Deposits which are formed can be removed
by wiping with a sponge.
In an immersion type system, the operator cannot
reach the bottom of the tanks and must rely upon chemical cleaning agents to
remove chemical deposits.
When the spray machine is used, milliliter of
solution can be filtered before it is repumped into the machine. Developer,
however, is oxidized rapidly and requires a large amount of replenishment. The
rapid exhaustion of the developer, and consequent high rate of replenishment,
makes the spray processor expensive to operate.
g. Other considerations are the man-hours required to mix this replenisher
and the storage space the replenisher occupies. Most processors used by the
Army are immersion machines.
4.
Recirculation Systems.
a. Recirculation systems perform four important functions in processing
machines. The recirculation system:
8
Previous Page
