When the signal device is installed with a 180-degree rotation, the toggle lever

(1) is positioned between the OPEN and SHUT indicator plates and points downward, keeping the signal device in a non-triggered state. As the valve gradually closes, the OPEN and SHUT indicator plates move upward. When the valve is fully closed, the long bolt 

(2) on the SHUT indicator plate pushes the toggle lever, causing the trigger rod to move and activate the microswitch, sending an electrical signal. When the valve gradually opens, the trigger rod resets under the spring's tension, disconnecting the signal.

When the valve is in a half-open/half-closed state, the signal device's toggle lever

(1) is positioned between the OPEN and SHUT indicator plates and tilts upward, keeping the signal device in a non-triggered state. As the valve gradually opens, the OPEN and SHUT indicator plates move downward. When the valve reaches 80%-100% open, the long bolt

 (2) on the OPEN indicator plate pushes the toggle lever, causing the trigger rod to move and activate the microswitch, sending an electrical signal. When the valve gradually closes, the trigger rod resets under the spring's tension, disconnecting the signal.