WHO'S GOT THE SCOOP ON RESIDUAL VALVES?

Wheel cyls came with springs.....

The purpose of the RLPV was to keep the wheel cyl seals slightly pressurised. This reduced the travel that the wh cyl pistons would need to move, & kept the height higher & more constant.
Many car makers started omitting the RLPVs because they really didn't do much......except increase costs.