Solenoid valve is mainly to power as energy, the current through the drive electromagnetic coil electromagnetic force, and then the electromagnetic force through the control of the spring to control the valve. Of course, this spring can be used to control both the closing valve and the opening valve. So based on this property we can either have the coil not energized when the gas circuit is closed, which is a Valvola di tipo normalmente chiusa (n/c), oppure possiamo avere la bobina non eccitata quando il circuito del gas è aperto, che è una valvola di tipo （n/o normalmente aperta .
