Weak/failing vacuum pump

cowman

cowman

Final Approach
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Cowman
Wondering if I have an issue.

After landing and turning off the taxiway this evening I noticed my Vac annunciations light was on- this isn’t that odd at idle but the I brought it up to taxi and the light remained on. Messed around a bit and found I had to bring it up to 1500 to get the light to go mostly out- it was still dimly lit. Vacuum gauge reads about 3.5 at 1,000RPM. No functional issues with any vacuum driven instruments, no indication of an issue in flight.

It’s not weird for that light to come on with the throttle pulled all the way back but at 1000RPM I think it should be off


Aircraft is a Piper Lance non-turbo.
 
Vacuum should settle at between 4.6 and 5.4"Hg. 3.5 is bad, and it could be due to a failing vacuum regulator, or more likely a worn-out pump. Might be a bad vacuum line, for that matter. Some older airplanes had sections of aluminum line that would corrode and develop holes that dropped the vacuum.

Don't buy a pump without the vane wear check ports. Rapco and Tempest make them. Fist check at 500 or so pump hours, then every 100 after that, replacing the pump when the wear check indicates. That way you're not experiencing a failed pump at a bad time.
 
Kinda figured, I've had one go before in flight and it was an all at once failure instead of a poor performance deal. So of course I put that one on, sell the airplane, buy a new airplane and have to do it again.
 
Or a leak in your vac system.
 
Most dry pumps blow apart all at once thought some do start to get weak. What you should however realize is that SOMETHING IS DIFFERENT. Don't make the fatal NASA mistake of accepting an unexpected but "within tolerance" change as the new "normal."
 
I've destroyed my share of vacuum pumps over time. They don't have a good MTBF, and the variance is high. I've had them go at 100 hours. At 500 hours you have to be on borrowed time. I'm planning on ripping my vac system out in the near future by putting in some G5s.
 
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