How does our brake system actually work? Options

[stugray]

I have witnessed one racing brake failure and recently heard about another one recently that is making me wonder about our brakes and how they work.

Based on the brake system schematic in the Haynes manual (page 110), it appears that our system has a "front circuit" and a "rear circuit".
It looks as if the front & rear connect to separate chambers in the master cylinder.
Each chamber is driven by a separate piston, but connected to the same shaft (they cannot move independently).

So if the above is true, then if you snapped off a front brake line (what happened to my brother) the front circuit would be dead, but the rear circuit should still be able to build pressure and stop the car (although not nearly as quickly).

Same goes for breaking a rear line, you should still have front brakes.

However this makes me ask two questions:
1 - How can you possibly put a brake bias valve into a system like that?
I thought brake bias valves worked by allowing you to divert more pressure to the front and less to the rear (or vice versa), but if the front & rear systems are completely independent, then this would not work.

2 - If one system remains operational if the other fails, then WHY does the pedal go to the floor if you open one bleeder valve?

Confused (IMG:style_emoticons/default/confused24.gif)