The 106-A-Type 1 and 206-A-Type 1 Altitude Control Valves are based on the 106-PG or 206-PG main valve, and are ideal for maintaining a preset maximum water level. The valve functions as a two-position control valve, either fully open or fully closed. The Type 1 allows normal forward flow to fill the reservoir to the maximum level and then closes drip-tight at the set-point. It opens to allow reverse flow through the valve when the supply pressure drops a fixed amount below the reservoir head. When a higher supply pressure is restored, the Type 1 valve will then allow normal forward flow to refill the tank to the maximum level.