How do they work in areas prone to brown outs? They work fine when working within the area of 18, to 31.5 volts. That would be considered an acceptable range. The maximum flow rate? I would use the Cv published on the submittal data sheet to calculate what the added pressure drop to your system would be? Always consider the 4’ per second rule for maximum velocity. 12 valves per transformer? We tested the Zone Sentry today with 12 valves powered by a 40VA transformer using a ZVC404 as a test to determine how long it would take to open the valves when operating 12 in parallel, and experienced a charging time for all 12 actuators between 42 and 47 seconds. The specification appears to be adequate.