2 MIN TURN DC ELEC L R 2 0 2 0 I 0 I 0 2 0 I 0 8 6 4 2 0 I0 PRESSURE Turn-and-bank indicator Pressure gage Altitude indicator Heading indicator Shaft Rotor Case Outlet Inlet Vane 10-50 Multiengine aircraft typically contain independent vacuum  systems for the pilot and copilot instruments driven by  separate vacuum pumps on each of the engines. Should an  engine fail, the vacuum system driven by the still operating  engine supplies a full complement of gyro instruments. An  interconnect valve may also be installed to connect the failed  instruments to the still operational pump.  for a short time. Thus, when combined with the aircraft’s  magnetic compass, sufficient attitude and directional  information is still available. Pressure relief valve—since a reverse flow of air from  the pump would close both the gate check valve and the  suction relief valve, the resulting pressure could rupture the  lines. The pressure relief valve vents positive pressure into  the atmosphere. Gate check valve—prevents possible damage to the  instruments by engine backfire that would reverse the flow  of air and oil from the pump.  [Figure 10-90]  Vacuum regulator or suction relief valve—since the  system capacity is more than is needed for operation of the  instruments, the adjustable vacuum regulator is set for the  vacuum desired for the instruments. Excess suction in the  instrument lines is reduced when the spring-loaded valve  opens to atmospheric pressure.  [Figure 10-89] Air-oil separator—oil and air in the vacuum pump are  exhausted through the separator, which separates the oil from  the air; the air is vented overboard, and the oil is returned  to the engine sump. This component is not present when a  dry-type vacuum pump is used. The self-lubricating nature  of the pump vanes requires no oil. Figure 10-87.  Simple venturi tube systems for powering gyroscopic instruments.  Figure 10-88.  Cutaway view of a vane-type engine-driven vacuum  pump used to power gyroscopic instruments.  Typical Pump-Driven System The following components are found in a typical vacuum  system for gyroscopic power supply. A brief description is  given of each. Refer to the figures for detailed illustrations.