Piper Comanche PA-24 Service Manual page 799

11-15. Vacuum Pump Removal.
The vacuum pump is removed by the following procedure:
A. Remove the top portion of the engine cowling.
B. Loosen the two hose clamps and remove the two hoses from the vacuum pump fittings. Identify the
hoses to aid in reinstallation.
C. Remove the four retaining nuts lock washers and plain washers.
D. Remove the vacuum pump.
NOTE: Before installation of fitting on pump, check for external dame. A pump that has been
damaged or dropped should not be installed. When a vise is used to secure pump while
installing fittings, suitable caution must be exercised to avoid pump damage. The square
mounting flange must be held between soft wood blocks and only at right angles to the vise
jaws. Use only enough vise pressure to hold pump firmly. DO NOT apply vice pressure to
outside diameter or overall length. The ports of the AIRBORNE dry air pump have been
treated with a dry film lubricant and the AIRBORNE fittings are cadmium plated thus
eliminating any need for thread lubricants. If a thread lubricant is required use a powdered
moly sulfide or graphite in dry form or in an evaporating vehicle; or employ a silicone
spray. Apply sparingly to external threads of fittings only. DO NOT use pipe tape, thread
dope, hydrocarbon oil or grease as these can contaminate pump and cause malfunction.
With pump properly secured in vise, insert fittings in ports and hand tighten firmly. Next,
using a wrench. tighten each fitting from one-half to two turns additional.
11-16. Vacuum Pump Installation.
The vacuum pump is mounted as follows:
A. Remove the top portion of the engine cowling.
B. Align spline on the pump drive with spline on the engine drive assembly.
C. Secure pump to engine drive assembly using four retaining nuts, lock washers and plain washers.
D. Connect the inlet and outlet hoses to their respective fittings on the vacuum pump using two hose
clamps.
E. Check all connections for security and reinstall the top engine cowling.
11-16a. Vacuum Pump. (Aero Accessories, Inc., Service Replacement.)
A single engine-driven dry-air pump is mounted on the accessory section at the rear of the engine. The
vacuum pump is a rotary vane, positive displacement type. These units consist of an
aluminum housing, a carbon rotor and carbon vanes. They are driven by means of a coupling mated to an
engine-driven gear assembly.
A. Inspection - Aero Accessories Tempest Pumps Only
The vacuum pump(s) feature a wear indicator inspection port on the back cover which allows direct
observation of pump vane wear. Beginning at 500 hours time-in-service, and each 100 hours
thereafter, remove the inspection port plug and observe vane wear as shown in Figure 1.
1. As the vanes wear, they slide outboard in the vane slots in the rotor.
2. When the portion of the vane that can be observed in the inspection hole covers approximately
1/8 of the inspection hole, replace the pump.
XI - INSTRUMENTS
PIPER COMANCHE SERVICE MANUAL
(See Figure 11-1.)
3F22
04/01/09