Originally posted by rhmimac How come that a water temp regulation is needed when the Jobo heats up the mix to the needed 38°C?
The drum with the film rotates and is slightly immersed in a bath that maintains the correct temperature. This bath also heats the chemicals (in separate containers that stand partly immersed in the internal bath).
But water for pre-soak, rinsing between chemical stages and final rinse/wash is taken from an external source. This can either be mains water from a temperature regulated supply (1-6 bar) and should ideally be either 24.0°C for B/W or 38.0°C for colour processing; or water supplied via a 12V pump from a basin containing water at the correct temperature. If the water supply is either too hot or too cold, this will show up as colours shifts with colour films and as too thin or too dense negatives in B/W processing.
Plumbing with a termostate controlled supply will add to the cost of the whole setup. Therefore a basin with 12V pump is a much easier solution.