MrCreosote
02-22-2021, 04:49 PM
I was under the impression that a BPV made the rear brake pressure proportional to front brake pressure and that the adjusting valve/spring determined this ratio.
WRONG:
The BPV has a fixed ratio and the adjuster/spring sets the transition pressure.
NOTE: one barely legible cutaway of a BPV revealed there are 2 bore diameters - I believe the arear ratio of those diameters establishes the proportion.)
Here is a test of a Willwood Variable BPV and here are the results:
So far, I haven't come close to finding a discussion and illustration of a BPV operation.
https://wilhelmraceworks.com/blog/brake-proportioning-valve
47005
Some Thought Doodles: (don't read following - no conclusion. If I figure it out, I'll unshadow it)
I know how you apply boost to the atmospheric side of the fuel pressure regulator to maintain FP ahead of BP in a blow through carb. The regulator spring adjusts the offset.
So starting with a traditional regulator, the spring setting would determine the max rear brake pressure - a zero slope after the transition.
So to get some "after transition slope" have to apply LESS "spring force."
Regulator Basics:
Spring pushes valve closed
Pout on side of diaphragm that closes valve (Pout gets big enough, balances spring, closes valve)
Consider the dual bore piston:
There will be a pressure ratio between the two piston faces that produces no movement.
This could be the mechanism which supplements the regulator spring - when the PR is achieved, there is only spring force on the diaphragm.
Which side pressures applied?: As more brake pedal applied, higher pressures, and greater "spring pressure"
The above would count for the parts in the BPV cutaway: dual bore piston, spring, and a valve.
PLAY WITH SOME NUMBERS:
@ TRANSITION:
120 psi on both sides of piston producing Ft resultant on dual bore piston. (BIG BORE dominates)
240in and 180out psi
WRONG:
The BPV has a fixed ratio and the adjuster/spring sets the transition pressure.
NOTE: one barely legible cutaway of a BPV revealed there are 2 bore diameters - I believe the arear ratio of those diameters establishes the proportion.)
Here is a test of a Willwood Variable BPV and here are the results:
So far, I haven't come close to finding a discussion and illustration of a BPV operation.
https://wilhelmraceworks.com/blog/brake-proportioning-valve
47005
Some Thought Doodles: (don't read following - no conclusion. If I figure it out, I'll unshadow it)
I know how you apply boost to the atmospheric side of the fuel pressure regulator to maintain FP ahead of BP in a blow through carb. The regulator spring adjusts the offset.
So starting with a traditional regulator, the spring setting would determine the max rear brake pressure - a zero slope after the transition.
So to get some "after transition slope" have to apply LESS "spring force."
Regulator Basics:
Spring pushes valve closed
Pout on side of diaphragm that closes valve (Pout gets big enough, balances spring, closes valve)
Consider the dual bore piston:
There will be a pressure ratio between the two piston faces that produces no movement.
This could be the mechanism which supplements the regulator spring - when the PR is achieved, there is only spring force on the diaphragm.
Which side pressures applied?: As more brake pedal applied, higher pressures, and greater "spring pressure"
The above would count for the parts in the BPV cutaway: dual bore piston, spring, and a valve.
PLAY WITH SOME NUMBERS:
@ TRANSITION:
120 psi on both sides of piston producing Ft resultant on dual bore piston. (BIG BORE dominates)
240in and 180out psi