Which one of the following describes a characteristic of pneumatic valve positioners?
A. They can provide automatic and manual demand signals to pneumatic controllers and valve actuators.
B. They can increase or decrease air pressure to valve actuators to obtain the proper valve response.
C. They can either supply or receive air to/from pneumatic controllers, depending on the direction of valve travel.
D. They can increase air pressure to valve actuators above existing main air header pressure.
Share your understanding of this question with the correct explanation.