Pressure control valve, The Model SC-1110 Modulating float control valve to maintain constant liquid level in storage tanks and reservoirs by compensating for variations in supply or demand, keeping the tank full.The Ball type float operated Pilot Control is installed at the high liquid level in the tankreservoir and is connected via tubing or pipe to the main valve. As the liquid level changes, the float control proportionally opens or closes the main valve, keeping the liquid level nearly constant.