Gosh Ignition Override I didn’t know I was going to get an oral on the DC-9 hydraulic system. Yes your source is correct on the exact numbers and wiring on the DC-9. The Transfer Pump will transfer pressure but not liquid. Depending on which side has more pressure will make one side a motor and the other side the pump there by pressurizing the other side. It does it in pulses and if you sit over the wing on the ground with one side unpressurized you can hear the Transfer pump making a thumping noise under your feet. But getting down to the brass tacks it is enough power to keep your brake system charged so you can stop the aircraft.
I’ve been told too that the Transfer Pump is the only place where the two systems come together. Ask your “source” if there are any hydraulic fuses or check valves on the brake accumulators to maintain brake pressure in the event of a complete loss of hydraulic fluid on either side?