Figure 1-8. Schematic of a typical immersion processing tank
b. Recirculation system (fig 1-9) performs four important functions in processing machines.
(1) Filters the solutions.
(2) Controls the temperature of the solutions.
(3) Provides a logical place to add replenisher to the solutions.
(4) Provides a certain amount of agitation to the solutions.
Filtration. Solutions are generally filtered before they are reintroduced into the machine. Solutions are
filtered and recirculated on a continuous basis during machine operation.
a. Filtration is accomplished through the use of screen or cartridge filters. The particle size passed by
the filters is very important.
b. Most processors use filters that will filter out all particles larger than 10 microns. Wash water must
be filtered to the same degree as the chemical solutions. Instruments used on the solution filter system should
include pressure gauges on the inlet and outlet of the filter to indicate the pressure drop across the filter system.
c. The pressure drop signals when the filters are becoming clogged and need cleaning or replacing.