Dead vacuum pump?

[redbaron1982]

40 minutes after take off today, the LO/HI VAC annunciator light illuminated and the vac gauge was reading zero, I was VFR on a VMC day, so no biggie. I turn on the standby vacuum pump, the anunciator light extinguished and the vacuum was back at 5in hg.

My understanding is that there is no other thing that can cause this that a failed engine driven vacuum pump. Am I correct?

The one I have installed is this one: https://www.aircraftspruce.com/catalog/pnpages/10-23925.php which goes for $454 brand new (no core exchange).

Am I analyzing this right? Any suggestion on staying with Rapco or moving to Tempest or other brand?

[EricJ]

Sounds right.   It's usually easy to tell whether the pump has failed by inspecting the drive coupling, which is externally visible so that it can be inspected.   The normal failure mode of the pump is that it seizes when the graphite vanes wear down to the point where they fracture, and then the coupling shears (by design).   It's easy to see if the coupling has sheared, and that's a sure sign that the pump has failed and needs to be replaced.