Hy Shellology and guys, the diagram for the drum/drum looks okay, but I have never used a metering valve in the front brake circuit, and there were millions of single systems used that did not employ or require such a valve. The system shown has the primary plumbed to the rear brakes, which is the way I would do it. It would appear that this company is only selling disc/disc master cylinders, that is the only reason I can see for installing separate residual pressure valves. Incidently I was taught that the purpose of residual pressure valves was to keep the wheel cylinder cups against the bore of the wheel cylinder, that would stop air/moisture from being drawn in to the wheel cylinder when you released your foot from the brake. Keeping the shoes up next to the drums is a function of the adjusters not the residual pressure valves, hope that helps.