A butterfly valve which transmits a signal or can provide some sort of indication when used of whether it's fully closed or not fully closed. Can anyone tell me where I could find one / what I'm after? I'm after about 3" diameter, I'd like to place them below a water cannon, and use them to provide a safety start (i.e. if someone tries to start the water cannon's pump, and all 4 valves are not shut (using 4 cannons currently), the pump doesn't start causing one or more cannons to discharge water in a random direction). Typically mechanical linkage to a valve positioner which is attatched to the stem will show the postion in a pneumatic flow control valve. You can buy some actuators that have associated pressure transducers. Once you program the controler to the given ranges, the controler in a digital system will show how open or closed the valve is. HOWEVER, there is a major downside to this. It is using air or hydraulics, it does not actually go on the real position of the valve. It goes off of what the pressure transducer is telling it. If the valve is sticking or the controller is not calibrated right, it will give a false reading.

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