In this area I have not seen any residential zone valves that use either 0- 10 v or 4 -20 ma.
They are modulating zone valves uses with a building control system usually in a commercial application. They may be open, closed or anything in between depending on what the controller wants. Instead of a switch there is a potentiometer that gives position feedback to the controller- 4 to 20ma loop current depending on the position.
-Hal
