Engine-Driven Vacuum PumpThe vane-type engine-driven pump is the most commonsource of vacuum for gyros installed in general aviation,GS3
Flux valve or flux gateDG/Amplifier or slaved gyroDirection indicatorFigure 10-86. Solid state magnetometers.10-48LR2 MIN TURNDC ELEC46PRESSURE2 80I020Altitude indicatorTurn-and-bank indicatorPressure gageHeading indicatorFigure 10-87. Simple venturi tube systems for powering gyroscopic instruments.light aircraft. One type of engine-driven pump is geared tothe engine and is connected to the lubricating system toseal, cool, and lubricate the pump. Another commonly usedpump is a dry vacuum pump. It operates without externallubrication and installation requires no connection to theengine oil supply. It also does not need the air oil separatoror gate check valve found in wet pump systems. In manyother respects, the dry pump system and oil lubricatedsystem are the same. [Figure 10-88]InletVaneRotorCaseFigure 10-88. Cutaway view of a vane-type engine-drivenvacuumpump used to power gyroscopic instruments.When a vacuum pump develops a vacuum (negativepressure), it also creates a positive pressure at the outlet ofthe pump. This pressure is compressed air. Sometimes,
it is utilized to operate pressure gyro instruments. Thecomponents for pressure systems are much the same asthose for a vacuum system as listed below. Other times, thepressure developed by the vacuum pump is used to inflate de-ice boots or inflatable seals or it is vented overboard.An advantage of engine-driven pumps is their consistentperformance on the ground and in flight. Even at lowengine rpm, they can produce more than enough vacuumso that a regulator in the system is needed to continuouslyprovide the correct suction to the vacuum instruments. Aslong as the engine operates, the relatively simple vacuumsystem adequately spins the instrument gyros for accurateindications. However, engine failure, especially on single-engine aircraft, could leave the pilot without attitude anddirectional information at a critical time. To thwart thisshortcoming, often the turn and bank indicator operateswith an electrically driven gyro that can be driven by thebattery for a short time. Thus, when combined with theaircraft’s magnetic compass, sufficient attitude anddirectional information is still available.Multiengine aircraft typically contain independent vacuumsystems for the pilot and copilot instruments driven byseparate vacuum pumps on each of the engines. Shouldan engine fail, the vacuum system driven by the stilloperating engine supplies a full complement of gyroinstruments. An interconnect valve may also be installed toconnect the failed instruments to the still operational pump.Typical Pump-Driven SystemThe following components are found in a typical vacuumsystem for gyroscopic power supply. A brief description isgiven of each. Refer to the figures for detailed illustrations.
You've reached the end of your free preview.
Want to read all 23 pages?
- Winter '18
- Vacuum, Compass, Gyroscope, Vacuum systems, Gyroscopic instruments , Aircraft Systems