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Question
1987 Cessna
182. Vacuum gage pulsates or vibrates on start up for about
15 minutes. By the time I’m ready for take off everything
looks good. Any ideas?
Harry C.
Des Moines, IA
Answer
Mr. C.
With all the components that can fail within your gyro system none can “repair” themselves
by the time you get to the end of the runway, except the air pump. The only
thing changing from the time you start your engine to the time you’re
ready for the wild blue yonder, is the temperature of your engine.
My thought on this is somehow either oil, cleaning solvent or moisture was
ingested into your pump.
The air pump interior contains carbon vanes positioned in slots in a carbon
rotor. As the rotor spins, centrifugal force throws the vanes out against the
interior wall of the pump housing to create a vacuum on the backside of the
vane. With the rotor spinning at a high rate of speed the 6 vanes create enough
vacuum in the system to eventually operate your gyros. The vacuum regulator
not only smoothes out these “pulses” of the pump into a steady
vacuum source but also regulates the amount of vacuum applied to your system
as the engine and pump may vary in speed.
The vanes are lubricated in the vane slots by carbon dust. This super lubricant
is fine for the purpose intended except when mixed with any liquid contaminate.
Take a little carbon dust mix in a little liquid and you get the blackest “honey
like” substance ever made. Add a little liquid to the pump interior
and the vanes start to stick within the slots. With one or two vanes not
producing a vacuum, the pump is now creating a pulsation in the system that
the regulator cannot correct. Thus, needle “bounce” or vibration.
If the contamination were water (condensation), running the engine several
minutes would evaporate the water, dry out the pump interior and your back
in business.
If the sticking vanes were cause by oil or solvent ingestion you’re
not as lucky. Pump replacement is the only answer, but only after you figure
out the source of contamination.
Cleaning Solvent - Cover the air pump coupling every time you spray clean
the
Engine.
Oil - Make sure:
1. You have a good air pump gasket at the pump mounting,
2. You don’t give the pump an oil bath when you change that old oil filter can.
Let us know what you find and Fly “Heads-Up”,
R. Heysek
Aerotech Components, Inc.
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