Residual Pressure Valve placement

Wow, He ask a question about the residual valve, did he not?
Photos show a proportioning valve.
The reply's are getting crazy.
The most of ya are correct when you say the "residual valve is in the master cylinder"
I have been a ASE master tech for over 35 years and never heard tell of a residual check valve in a wheel cylinder. What would happen if you only changed one rear wheel cylinder?