GB915948A - Liquid level control means - Google Patents

Abstract

915,948. Automatic liquid level control. AUTOMATIC CANTEEN CO. OF AMERICA. Oct. 19, 1960, No. 35824/60. Class 38 (4). In a system for automatically controlling the level of a liquid in a tank, a relay switch is actuated by the operation of a relay winding to effect the supply of liquid to the tank and a shunt circuit, including an electrode disposed in the tank, is connected across the relay winding and is opened to render the winding operable by the liquid breaking contact with the electrode when the liquid level falls below the lower end of the electrode. As shown, a tank 1 of a coffee vending machine has an insulating lid 17 through which projects electrodes 19, 16. A delivery pipe 26 protrudes into an opening 27 in the lid and the admission of liquid is controlled by a solenoid-operated valve 23 energized from a supply 3, 4 through contacts 13 of a relay 10. The relay is energized through an isolating transformer 2 and a capacitor 7 arranged to form a series resonant circuit with a relay coil 9. When the level of the liquid is below electrode 19, the relay 10 is energized so that contacts 12 isolate the electrode 19 and contacts 13 energize the valve 23 to allow liquid to flow to the tank. When the liquid touches the electrode 16 the relay coil 9 is short-circuited by the liquid, contacts 13 being opened to close valves 23 and contacts 12 closed to connect the electrode 19 to the relay coil circuit. The electrode 19 maintains the short-circuit across the relay coil until the liquid level falls below the electrode. The relay is then energized and the relay 10 and valve 23 are cycled to maintain the level of liquid between the limits set by the electrodes. In a modification, the electrode 16 is dispensed with and the valve 23 is energized through contacts 13 for a period determined by a motor-driven time-switch. After one rotation a switch is closed by a projection on a drum to short-circuit the relay 9. The time-switch is reset by the over-run of the motor rotating the projection past the switch.