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Saturday Afternoon
3/8/08
Giff Marr,
I never saw a response to your question where the cabin pressure annunicator was done like mine, so hopefully my suggestion is worth considering.
We used a Pressure Controls, Inc. (http://pressurecontrols.biz/) Model AV-1 Altitude Switch, which we installed in the cabin area ( round silver switch in photos attached). This switch is set for 10K feet and is connected so the light on the annunicator panel (photo attached) will illuminate when the cabin pressure exceeds 10K feet. As long as the cabin pressure stays below 10K feet, the light should not illuminate.
We also used an identical switch for our boost pump annunicator, which will illuminate when we climb through 10K feet. When we turn on the boost pump on low, the light will go out. Whenever we descend back through 10K feet, the light will illuminate again and turning off the boost pump will extinguish the light. I have a schematic that a friend of mine drew for this circuit and would be glad to share it with you if you elect to do something like this for your IV-P. We installed this altitude switch in the right wing root under an access panel we had made for connecting the speed brake cable. As long as you are sensing atmospheric pressure, location doesn't really matter. The wing root access cover gives us easy access - four screws and you have it in your hand.
At the time I bought the altitude switches (June '06), the price was $250.00 each. Pricey, but is a high quality switch.
Regards,
Ed Smith
N9JE (IV-P)
Chesapeake, VA
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