45-degree Angle for Ball Valves

Somebody told me to leave the ball valves on my backflow preventer at a 45-degree angle (or the half open-half closed position). Why?

Answer:
In the normal operation mode, they should be fully open. However, after the system has been winterized the ball valves on the backflow preventer are supposed to be at a 45-degree angle.

In the winter months (when the system is not in use and has been winterized) condensation can be trapped in a fully open or fully closed valve. This usually occurs between the ball and the body of the valve. In freezing temperatures the water will freeze, thus cracking the valve.

Again, only in the winter months after the system has been winterized should the ball valves be left at a 45-degree angle.