Most modern airplanes come equipped with at least one vacuum pump. This device either draws or pushes air that powers the various gyroscopic instruments.
In a traditional instrument setup, the attitude indicator and heading indicator are driven by the vacuum pump, while the turn coordinator is powered with electrical power.
There are two basic types of vacuum pumps—wet and dry—although each works more or less the same way. Wet pumps use oil as a lubricant, while the more common dry pumps are considered self-lubricating.
In either case a metal outer shell houses a rotating cylinder made of either a carbon material or steel. Slots are machined into the cylinder to accommodate carbon-based fins or vanes, which basically are small rectangular pieces that can move freely within the slots. The cylinder is directly attached to a rotating shaft that is geared to fit into an accessory case on the engine. As the engine runs, it turns the shaft, which turns the vanes. The housing is bigger than the cylinder and vanes, allowing them to be thrown out against the inside wall as they spin. The vanes then compress the air and direct it to an opening in the housing where a hose is attached between the pump and the instruments.
