I think you are mistaking where the low level sensor is. The main tank is approximately
75 gallons. The low level sensor is set at around the 60 gallon level.
The plane burns 1.5 to 2 gallons per minute at non takeoff settings, so the
valves would typically cycle every 7 to 10 minutes. If the fuel gets below the
low level sensor for longer than 20 seconds the low level light would come on
giving you around 30 minutes to land.
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http://forums.matronics.com/viewtopic.php?p=516879#516879
