One of the most common technical calls VAC receives is dealing with tubing a positioner for single or double acting applications. The V100 and V200 can be tubed up as double acting or single acting. When the unit is tubed up single acting the C- port needs to be plugged. Remember that on increasing control signal air is always exhausted out of the C+ port. A simple way to check to make sure that your tubing is correct with the V100 or V200 is to push down on the balance arm inside the positioner. If nothing happens when you push down, it’s an indicator that the tubing is incorrect.
The D400 and D500 is a little bit different. They can be ordered as single acting or double acting. If the unit is ordered as a single acting unit, it CANNOT be used as a double acting positioner. However, if you order the unit as double acting, the unit can be used as a single acting by plugging the OUT 2 port. A double acting D400 or D500 will also improve your standardization on just having one unit that can cover both single and double acting applications.