Brakes - prop valve, understanding?

[FirstGen]

Just wanted to know what a 2 inlet 2 outlet prop valve is doing? Like the ones on our trucks. Maybe a front disc truck is different but mine (68) is a 4 port design. Anyone understand the exact mechanics behind this? I would think that you would want only a prop valve for the rear brakes and full flow on the front? I am guessing that I am wrong since most factory valves are 4 port, even today...

Help me out here.

[Longhorn Man]

Your truck doesn't even have a proportioning valve. That is nothing more than a ditribution valve and a pressure switch. It's main job is to turn on the dash light if there is a problem.

[FirstGen]

So basically that huge block does nothing more but to monitor both lines in case of pressure loss? I guess I'm gonna "shave" that then if that's all it does!