These are divided into 3 major groups, depending on the service you want:

Drive On – OFF (Class A): The actuator must bring the valve in the entire operation from the fully open position to the fully closed position and vice versa. The denomination for these computers SA / SQ.

Positioning (Class B): Inching or positioning service. The actuator must carry the valve
from time to time at a position, any position (fully open, intermediate position and fully closed position). The denomination for these computers SA / SQ.

Modulating / Regulating (Class C): The actuator must carry the valve regularly to a position any
between the fully open position and fully closed position, being able to modulate from 1% to 100% (opening closing). The denomination for these computers SAR / SQR.