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Driven, if you are referring at all to my post yesterday at 4:48, I take it all back. Delete. I was just going along with the logic of skinnyG and M-V8; I know NOTHING about prop valves.

Driven and Skinny are correct.

The valve is open below the actuating point so there is no difference in pressure under conditions where weight transfer is minimal.

The actuating point is usually adjustable from less than 100 psi to around 1,000 psi.

Being able to stop faster from reduced curb weight or better traction should have a lower actuating point.
Moving the cg aft ( i.e. 60/40 toward 50/50 or 50/50 toward 40/60) should have a higher actuating point.

My referrences are from the "Brake Handbook" by Fred Puhn.

Actually my response was largely to Skinny's description too, where he says:

It's the spring inside that seats the valve, and brake pressure will have to overcome spring pressure before it can apply the rear brakes.

But I'm glad to see support that I have been correctly interpreting what I've read on prop valve function.

Trust the links I posted, don't trust my description.

I remember when there was no automotive info online. Somewhere between then and now, I formed an opinion on this and stopped looking for more info.

I was trying to get my head around how a prop could "absorb" some of the pressure without having a return to the resevoir and not be a restriction. With a restriction, time becomes a factor because if a given rate of decelleration is maintained long enough, the pressure would equalize front and rear. I made a few searches and found this:

http://www.babcox.com/editorial/bf/bf50014.htm

It is the most detailed info I've seen on the actual operation with cutaways. It refers to the piston as being a fluid restrictor under hard stops. At full piston travel, it becomes a pressure limiter to the rear.

I think we all learned something here.

Excellent link, thanks