The 106-A-Type 4 altitude control valves are based on the 106-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 4 allows normal flow to fill the storage tank to the maximum level, then closes drip-tight at the set-point. It opens to refill the tank once the level drops an adjustable amount below the high water level.