Debris in Vacuum Pump Exhaust?

After the big 25 state trip, it was time to wash all the bugs off and - coincidentally - it was time for an oil change. So, while everyone at Bremerton was flying yesterday, I was in the hangar with a cold one, getting the maintenance done.

When I went to remove the oil filter, I noticed a lightly stained/dirty spot, about the size of a nickel, on top of the filter case. It was right where the discharge from the vacuum pump points to; the discharge fitting is a couple inches above the filter case. I was able to easily wipe off this light coating of debris/dirt, or whatever it was.

Question: is it logical to assume this came from the vacuum pump? And, if so, does it signify pump vanes that are getting ready to fail, or are failing? The pump has 271 hours on it. Vacuum readings on the cockpit gauge remain steady at all times. And, although my DG seems to precess more than it should (or at least I have noticed this over the last several months), I would think that is a DG issue, rather than anything to do with the pump itself.

[aeronut67]

The debris is carbon dust from the vacuum pump vanes and is normal. Depending on the manufacture there is sometimes an inspection hole to view how far the vanes have worn. If you cant see the vane in the hole its time to replace the pump.
http://www.aeroaccessories.com/servi...stnewpumps.pdf
Good luck, Glenn

[Jimd]

John,

Does your suction stay the same even when you throttle back to Idle or below 15 inches? Mine has dropped pretty low whenever I throttle back below 15 and it has done it since new? (Sorry for straying off your initial question)

Jim

[zilik]

Originally Posted by aeronut67

The debris is carbon dust from the vacuum pump vanes and is normal. Depending on the manufacture there is sometimes an inspection hole to view how far the vanes have worn. If you cant see the vane in the hole its time to replace the pump.

Good luck, Glenn

I never remember seeing any dust on my filter for the first 1150 hours but then it started dusting the filter ever so slightly. It got pretty bad so I decided to do something about it. I ordered the basic kit from ASC and proceeded to tear my old one down. Inside I found that everything is made from carbon. The rotor, vanes and housing. The vanes were were only .015 shorter than the new ones supplied in the kit. What was causing the dust is the sides of the vanes were wearing on the slots in the rotor causing the dust. I figure eventually the vanes would stick and not be able to retract as the rotor spun and they would break off. It was a real pain in the arse to overhaul and works exactly the same as before except for no dusting of the filter.

Thanks for the feedback. Sounds as though I just need to keep an eye on it, both the cockpit gauge and the oil filter, and see if any trends are developing. I am VFR only and so the vacuum system is not, at this point, a flight safety issue (I don't think).

JimD, I know my guage drops way down when at idle, but at 15 inches I am pretty sure it is still in the green - I will take a look though, next time I do a runup.