Control system for controlling the pressure on chocolate refining machine roll bearings

In a chocolate refining machine having a feeding roll pair and more than one refining roll located downstream of said feeding roll pair, each of said refining rolls being supported by bearings, a dual-function control system for controlling the pressure on the refining roll bearings for accomodating chocolate pastes of varying plasticity and fat content comprising a linked multi-pressure control circuit for said refining rolls comprising a hydraulic control unit for acting upon the bearing of each refining roll, a double-acting hydraulic pneumatic pressure step-up device having a hydraulic chamber and a pneumatic chamber, a first pressurized air conduit means connecting the hydraulic chamber of the related step-up device and hydraulic unit, a pneumatic regulator pressure regulator associated with each step-up device, second pressurized air conduit means connecting the hydraulic chamber of the related step-up device and pneumatic pressure regulator, there being a source of pressurized air, third pressurized air conduit means common to each of said pneumatic pressure regulators connecting each of them with said pressurized air source, there being a complementary linked single pressure control circuit for said refining rolls comprising a first hydraulic liquid conduit connected at one end with said second pressurized air conduit means between each pair of related step-up devices and pressure regulators, a hydraulic liquid manifold, each of said first hydraulic liquid conduits being connected at the other ends thereof with said manifold, a liquid pressure regulator, means connecting said hydraulic liquid manifold and said pressure regulator, a second hydraulic liquid conduit connecting said hydraulic liquid pressure regulator with said source of hydraulic liquid, there being a multi-positional selector valve interposed between said source of pressurized air, on the one hand, and the linked multi-pressure control circuit and said linked single pressure control circuit, on the other hand, whereby with said selector valve in one operating mode, said linked multi-pressure control circuit is energized, and with said selector valve disposed in another operating mode, said linked single-pressure control circuit is energized.