My bleeder pressurized both reservoirs with the same pressure. That won't
move the spool valve. Pumping the brake pedal sure will.
Jim Hupy
As soon as one opens a bleeder, the pressure would drop on that side making it lower than the other side of the combination valve.
When not bleeding, with the gauge attached, if it doesn't block it completely, the pressure would rise until it matches the pressure at the master cylinder.
It either blocks it completely and you can't bleed the brakes, or not completely and the pressure will equalize.
What you are implying is the pressure bleeder pressurizes the lines to such a low point that the shuttle doesn't move enough to shut off the flow to the low pressure side.
But what it all comes down to, if what Mr. Henderson is proposing is reality, you can't pedal bleed a system with that PV4 combination valve. At least not one wheel at a time. You would have to open a bleeder on the front and rear at the same time, or the "shuttle", which is a switch piston in the manual, would shut off the flow to the wheel you are trying to bleed.