The air flows to actuator when solenoid valve is energized, and the air is vented from actuator when solenoid valve is deenergized(reverse case available).
How Solenoid Valve Works?
1-way or 4-way valve is applied in case of emergency isolation of control valve, however 2-way valve is applied to block the air signal by electric signal, and 3-way valve is applied to emergency isolation or emergency opening of diaphragm actuator or single acting actuator. 4-way valve is applied to dual acting actuator.
We can arrange as below picture if we have to install all accessories in turn.
In case of small size valve, solenoid valve is applied if the fast vent is required since the vent from positioner is made slowly.
The location of lock-up valve is usually installed nearest to the actuator.
Author - Stanley Park