Automatically replenish evaporated liquid levels and control those levels in single tanks, reservoirs and sumps with this handy kit. Onboard air pressure-activated electrical switch opens a solenoid valve when liquid level drops by 1 in. and closes when liquid rises above its original level. Safe low voltage operation automatically turns off during power failures. Provides a significant advantage to traditional shut-off valves by maximizing the duration of RO or RO/DI units' membrane operation for extra pure water. Includes a safety backup float.