Method and system for controlling a compressed air flow in an air drier

Claim 1

Apparatus for controlling a compressed air flow from an air compressor to either one of two drying towers of an air drier, said apparatus including: an air-operated switch-over valve between the air drier and the compressor, an air-operated unloader valve being arranged between the switch-over valve and the compressor, an electric pressure switch downstream of the air drier for sensing air drier outlet pressure, the air for operating the unloader valve passing through a first, electrically controlled pilot valve and the air for operating the switch-over valve passing through a second, electrically controlled pilot valve, control means for controlling the positions of the first and second pilot valves, the control means including an electronic control device and the pressure switch, the electronic control device being responsive to the time the pressure switch is open, wherein the arrangement is such that voltage is supplied to the first pilot valve for directing operating air pressure to the unloader valve through one of the pressure switch, which is closed when the pressure at the drier outlet is at a predetermined level, and the electronic control device during periods of prolonged continuous air loading from the compressor through the air drier in the absence of operation of the pressure switch after a predetermined time, and that voltage is supplied to the second pilot valve for directing operating air pressure to the switch-over valve in a period from one to a next subsequent commencement of voltage supply to the first pilot valve and voltage is not supplied in the period from said next subsequent to the second subsequent commencement of voltage supply to the first pilot valve for allowing the switch-over valve to return to rest position.