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We have the same problem in a non-pressurized IV.  At higher altitudes it does the exact same thing.  We fly for almost  an hour and the same sequence occurs.  We just pull the breaker and it never leaks down.  I think the pump is marginal on pumping pressure with the decrease of air density; therefore, it  just can't reach the switch pressure.  Typical flights are FL180 to FL250.

Regards, Timothy Ong

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