The way I understand the "BV" (bypass valve) part of the LSPV-BV is that if you lose the front brake pressure, all it does is override the LS (load sensing) part of the valve, giving you the full amount of rear brake pressure that the PV (proportioning valve) part can send out. So with the manual PV, you just have that part of the system, there is no LS part and the BV part is simply eliminated, you have rear brakes and front brakes. If the fronts go out, you still have the rears. I ran for years with the load sensing arm tied up to the floor boards:
- http://www.4crawler.com/4x4/4R_suspension.shtml#ProportioningValve