Many solvent cleaners today work on a "batch" principle and the cleaning solution in the machine will eventually become contaminated with soluble substances and will therefore lower the efficiency of the cleaning operation. Replacement with fresh solvent is necessary to maintain high standards of cleaning and in the most recent machines, this is carried out transferring the dirty solvent to a distillation chamber and returning it to the cleaning tank after distillation. Batch distillation and circulation of the solvent with the cleaning tank connected to a separate distillation unit is still used in a few large film laboratories.
Cleaning machinery requires regular and high quality maintenance.
Regular checks should be made on the colour of the fluid and if the colour shows that it is contaminated [colour is one of the best indicators] the machine will need to be cleaned out and then replenished. A single roll of film with a varnish lacquer can seriously contaminate a solvent bath.
Rollers, filters and pipe works must be checked to make sure they are clean and changed where necessary. As with any transport system badly maintained cleaning machines can scratch film and so, film of no importance should be used as a test roll.
Ventilation and extraction units: are essential so they must be checked to make sure they are efficient.