This 3 wire connection is the basic connection. 

Keep your 12 V 1.5Amps power supply ready. 

Connect the 12V +ve to the Red colour wire.

Connect the 12V -ve to the Black colour wire. 

Connect the Green wire to the 12V +ve whenever the valve needs to be opened. 

This supply to the green wire can be given thru PLC, Relay Float switch.

As long as you need to open the valve, the green terminal should be connected to +ve 12V DC.

Note: Since the valve is stay put on power failure type. Red and black to be connected to positive and negative of 12V DC always.

Power consumption during valve close is zero and open is around 20mA. Actual power consumption takes during the movement of valve.