Piper PA-24 Comanche, Service Manual, Page: 797 / 846

PIPER COMANCHE SERVICE MANUAL
XI - INSTRUMENTS 04/01/09
3F20
11-9.
Gyro Service Procedure.
CAUTION: PERMIT NO OIL, GREASE, PIPE COMPOUND, OR ANY FOREIGN MATERIAL TO
ENTER PORTS, PRIOR TO INSTALLATION OF FITTINGS. MAKE SURE THAT ALL
AIR LINES ARE CLEAN AND FREE OF FOREIGN PARTICLES AND/OR RESIDUE
BEFORE CONNECTING LINES TO GYRO.
11-10.
Gyro Installation Inspection.
The following inspections should be made before removing a suspected gyro instrument from the
airplane.
Visual Examination:
A. Has the instrument been modified?
B. Has the instrument been damaged?
C. Does the instrument show any signs of abuse?
NOTE: Do not cage directional gyro and set to different headings. The entire gyro and fixture must
be rotated 90 degrees each time without touching the caging knob. If gyro is not rotated
and the caging knob is employed, the gyro is not repositioned in the case, only the card is
turned, this results in checking the gyro only in one position no matter how many headings
the card may be set to.
11-10a.
Gyro Handling And Shipping.
The following information applies to all three inch directional gyros and attitude horizon instruments
installed by the factory or a Piper field service facility.
Gyro instruments being returned to the factory are to be placed in approved container with all ports
properly sealed immediately after removal from the aircraft instrument panel. The instrument must also
be accompanied by factory copies of the warranty and credit claim forms. These forms and the special
containers should be available at any Piper Dealer and/or Distributor. Should any gyro instrument be
received by the factory in an unapproved container or if the ports are not sealed, the warranty will be
immediately voided and the instrument returned to the sender. The instrument must be returned
immediately after removal from the aircraft (not to exceed 15 days following discovery of defect).
11-11.
Vacuum System.
The vacuum system employed to operate the gyro instruments is comprised of an engine driven vacuum
pump, oil-air separator, vacuum regulator valve, and the necessary cubing to complete the system. On the
late model Comanche a dry vacuum pump has been employed. When this type pump is installed the need
for the oil-air separator and the hardware necessary for its installation is eliminated. A kit (P/N 754-356)
is available for installation of the dry vacuum pump on any of the early model Comanches.
One vacuum regulator valve is incorporated in the system to control vacuum pressure to the gyro
instruments. Access to this valve for maintenance and adjustment is gained through the engine cowling.
On the early model Comanche, the regulator valve was mounted on the firewall, while the later models
have the valve installed on the engine mount assembly.