I had to replace the valves that control the flow of ink and makeup because they were not completely sealed so that the fluids could flow back in the lines over time which would mess up the amount of added fluid for keeping the ink at the right viscosity.

Here is the old setup with two solenoid valves and one vacuum petrol tap per fluid.

And here is the new setup with just one solenoid valve per fluid. The valves are rated for petrol, diesel, and oil, so ink and solvent, water or acetone based, should also work as long as it is free from particles.

This also reduced the parts needed for building the cij printer - less cost and complexity.