Vacuum pump

[SteveG]

With regard to Jerry's suggestion to inspect the pump for a failed pump coupling, it seems that the only likely cause for a broken coupling would come from a broken vane causing the pump to seize and in turn causing the coupling to shear, which it is designed to do to prevent engine gear train damage. I presume Jerry must have encountered a broken coupling on an otherwise servicable pump at least once but I'm wondering if others have had similar experience and this condition is more prevalent than I would have assumed. Also, I doubt that if confronted with a sheared coupling on a pump with more than a couple of hundred hours of run time I would elect to repair rather than replace a $300 pump after investing the time and effort to remove it, replace the mounting gasket and reinstall. The difference between the cost of the coupling plus the time to repair and the cost of outright replacement being insufficient to justify reinstalling a pump with half its service life already exhausted. With respect to instrument contamination, this seems highly unlikely in a suction system as opposed to a pressure system. As to a better alternative, Airwolf is now selling an oil lubricated pump. I have no experience with it but I doubt that I could justify the additional cost in a pneumatic system with redundency such as ours although it might make sense in a single pump application rather than installing a backup vacuum solution.