OK, so the vacuum is taken care of by the electric pump, that's why they abandoned the big tank.
The Hydrovac is also abandoned. It would have had a fresh air line on the back if the cannister and a vacuum line attached to the control valve on the hydraulic side. When the hydraulic brake line at the Hydrovac sees pressure (you stepped on the brakes) the vacuum valve opens and the air is sucked out of the one side of the cannister and fresh air at 14 psi on the other side pushes the piston (in the middle of the cannister) into the Hydrovac's MC applying more pressure in the brake lines...vacuum assist! Sorry for the loooong sentence...LOL.
Mike B
