[Al Skierkiewicz]

If parts move with or without power, it is bad regardless of it being caused by electrical or pneumatic action. The vent plug valve, like that main circuit breaker, attempts to insure that no action on a participant's part will cause unexpected robot movement. We all know that the more wear a part gets, the more it is likely to leak air. In your example, should a actuator be locked due to an external valve and either the valve fails or the tubing goes open, movement will occur. This could be a violent action depending on the failure. We have all witnessed team members working on pneumatics, pull a tube while pressurized or cut into a tube while trying to use wire cutters to trim a wire tie or wire.