Aircraft Maintenance TroubleShoot > vacuum pump troubleshooting
Early vacuum pump failure. Short pump life
Dry Pump Systems
Inside a failed 211CC vacuum pump. Vanes and rotor are made from carbon.
1. Wrong part number pump installed on aircraft. For a quick check for proper pump rotation, manually turn the propeller a few degrees in its normal direction of rotation and watch the AND 20000 pad drive. If the drive turns clockwise, a clockwise (CW) rotation pump is required. If it turns counterclockwise, a counterclockwise (CC) rotation pump is needed.
2. Liquids entering pump cavity. End of vacuum pump should be sealed when washing down aircraft. The Airborne dry vacuum pump uses carbon vanes and a carbon rotor. Any liquid turns the carbon dust to paste. This past locks the vanes into the rotor cavity. This is a common type of failure.
3. Poor pump overhaul. The cavity of a normal worn-out vacuum pump will have a worn cavity. If the pump is overhauled with new vanes and carbon rotor and installed into the worn cavity, the pump will shortly fail. The carbon vanes strike the chatter wear marks on the cavity causing carbon chips to break off the vanes. When one of these carbon chips lodges between the rotor and cavity the rotor shatters.
4. Pressure pumps used on pneumatic systems. If the deice valves stick partially closed at completion of the deice cycle they cause excessive pump back pressure and operating temperature which leads to premature pump failure. This condition can exist when the deice system appears to be functioning properly.
5. Inaccurate gyro vacuum or pressure gauge. Gauges are never checked for accuracy, but they should be.
6. Carbon particle contaminates from the previous pump failure. Once the pump fails, if the pressure in the nacelle where the pump outlet is located is higher than the cabin then carbon particles from the broken rotor and vanes in the pump are sucked down the lines. When the new pump is installed it can suck particles from the inlet filter back into the new pump.
7. Teflon tape ingested into pump. Ever since their was a dry vacuum pump the manufacturer's have warned against using Teflon tape on the fitting threads. The pump housing is thin and the fitting threads protrude thru the housing. Teflon wrapped threads then are inside the pump housing where if they break off will seize the carbon rotor.
| Piece of Teflon tape If a piece of Teflon tape finds its way inside the pump it seizes the rotor causing the pump to fail. Teflon tape does not belong anywhere on an aircraft engine
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8. Deice pumps, on some systems the deice system only cycles to "off" when after pressure has reached a maximum. Holes in boots allow enough leakage that the activation pressure is never reached and the pump continues its futile attempt to meet the required pressure.
9. Twin-engine. If it is not providing pressure for its share of the load, the pump on the opposite engine is being overworked and will experience increased temperatures and a shortened life.
10. Attempting to repair a vacuum pump by installing new carbon into a old pump cavity.
Notice chatter marks on pump cavity. If you install a new "carbon kit" into an old cavity with chatter marks then the carbon vanes will fail. Check your housing before attempting to repair a vacuum pump by installing new carbon. If the housing is worn out or has chatter marks then replace the housing or better yet purchase a professionally overhauled or new pump.
Wet Pump Systems
1. Leaky oil seal in vacuum pump adapter pad. This seal can leak oil directly into pump causing excessive oil and short pump life.
