PURPOSE: To achieve the safe operation of a control system even if the cutting- off of an input electric signal is generated, by turning an air pressure opening means ON when the input electric signal reaches a rating value or less to release air pressure while shaking off outpt to a zero direction.
CONSTITUTION: An air pressure opening means 12 for performing the ON/OFF operation of nozzle back pressure is provided to an air pressure line between a nozzle 3 and a pilot valve 4. In this case, when an input current Ii reaches a predetermined value or more, the means 12 is turned OFF to perform usual control operation and output air pressure corresponding to voltage Eo' applied to a piezoelectric element flapper 2 is discharged. On the other hand, when the current Ii reaches a predetermined value or less, the means 12 is turned ON to release the back pressure of the nozzle 3 and the output pressure from the pilot valve 4 is forcibly shaken off to a zero direction. As a result, even if the cutting-off of an input electric signal is generated, a control system can be safely operated.
TAKADERA KENKICHI
ENOKI KOUICHI
