Troubleshooting the aircraft vacuum system

1. Vacuum Pump Troubleshooting www.mechanicsupport.com Pumps don't just fail - they are caused

2. Old Age typical vacuum pump lasts 600-800 hours. If your pump fails before this then the problem is most likely in the system and not the pump. Vacuum Pump Failure Contamination High air pump pressure (the gyro instrument vacuum gage DOES NOT display air pump pressure)

3. Contamination Carbon from previous pump Your pump has carbon vanes and a carbon rotor that often break apart into small pieces as the pump fails. When the pump stops pumping then the higher pressure in the engine compartment causes the carbon chips to be blown upstream into the hose. When you install the new pump then these bits of carbon are sucked back into the new pump where they jam between the carbon rotor and housing causing it to fail. Always clean out the hose when replacing the pump. These chips can also end up in the vacuum regulator where they wedge under the valve diaphragm. If the vacuum increases and decreases with changes in engine rpm then suspect that debris are wedged between the bottom diaphragm washer and the diaphragm seat. Raise the diaphragm using a thin blunt tool, remove the contaminant, and reset the regulator to manufacturer's service manual specifications..

4. Oil and Liquids Oil and liquids can enter the pump through the drive coupling. When you remove the failed pump, look into the ports to see if there is any wetness inside the pump. Oil mixes with the carbon inside the pump causing a sticky paste that will result in low pump output and eventual failure. Be sure the oil hasn't traveled into the hose. Liquid contamination is often caused by engine oil leaks and cleaning the engine with a high-pressure spray directed at the vacuum pump. Contamination Fittings are installed dry with no thread sealant or Teflon tape. This pump failed when bits of Teflon tape were ingested into the pump.

5. High Air Pump Pressure Any malfunction in the vacuum system that causes the pump to put out more pressure causes more wear and decreases pump life. There is no cockpit gauge that measures system pressure so a problem in the system goes unnoticed. The cockpit vacuum gage measures pressure drop across the gyro and is typically set at 4.7 to 5.2 inches hg (2.35 to 2.6 psi). If the pressure drop is low and you adjust the regulator you will place more load on the pump and shorten pump life. Adjusting the regulator does not fix the problem. Carefully inspect system hoses and fittings for leaks and obstructions. Further troubleshooting requires specialized testing equipment. System pressure check is done using the Cv-700 Pneumatic Test kit from Aerotech Components. www.aerotechcomponents.com Pump troubleshooting resources: www.aerotechcomponents.com