Piper PA-24 Comanche, Service Manual, Page: 798 / 846

PIPER COMANCHE SERVICE MANUAL
04/01/09 XI - INSTRUMENTS
3F21
11-11a.
Hoses and Clamps
A. These items should be examined periodically and inspected carefully whenever maintenance
activities cause hose disconnections.
B. Ends of hoses should be examined for rubber separation and slivers of rubber on inside diameter of
hoses. These slivers can and do become detached. If this happens, the loose particles will migrate
throughout the system and may eventually contribute to a failure.
C. Replace old, hard, cracked or brittle hose. Sections of the inner layers may separate.
D. Ensure hoses are clear and clean by blowing them out with shop air. Remove from aircraft as
required.
CAUTION: DO NOT WIGGLE HOSE FROM SIDE TO SIDE DURING INSTALLATION.
WIGGLING COULD CAUSE PARTICLES TO BE CUT FROM INNER WALL OF
HOSE WHICH CAN LEAD TO DAMAGE OF OTHER COMPONENTS.
E. Where hose clearance is tight, making it difficult to reinstall it onto a fitting or barb, spray the
fitting or barb with silicone. Let dry, then install hose by pushing it straight on.
CAUTION: WHEN REPLACING ANY THREADED FITTING, DO NOT USE PIPE DOPE,
THREADLUBE, OR TAPE. USE ONLY SILICONE SPRAY, LETTING IT DRY
BEFORE ASSEMBLY.
F. Hose clamps and fittings should be replace when broken, damaged or corroded.
11-12.
Vacuum Regulator Valve Removal And lnstallation.
To remove the regulator valve in the engine compartment, disconnect the three lines, remove the
mounting screws and remove the valve. Install regulator in reverse order given for removal. After
installation check complete vacuum system for leaks and proper operation.
11-13.
Adjustment Of Vacuum Regulator Valve.
To adjust the regulator valve, perform the following steps:
A. Loosen the locking nut or remove the protective cap from the valve, depending on which type is
installed.
NOTE: Do not attempt adjustment of this valve with the engine in operation.
B. Start the engine. After allowing time for warm-up, run the engine at medium RPM.
C. With the engine running at medium RPM, the suction gauge should indicate between 4.2 and 4.7
inches of mercury. Units with a central air filter system should indicate between 4.8 and 5.1 inches
of mercury. If the vacuum reading fails to fall within this range, shut down the engine and adjust the
regulator valve. Move the valve adjustment screw clockwise to increase the pressure and
counterclockwise to decrease the pressure. Start the engine and repeat the check.
D. After the system pressure has been adjusted to the recommended settings, retighten the locking nut
or replace the protective cap.
11-14.
Vacuum Pump.
(Original Equipment)
The vacuum pump used on the Comanche is the rotary vane, positive displacement type. The unit
consists essentially of an aluminum housing containing a tempered sleeve in which an offset rotor, with
moving blades, is incorporated. This assembly is driven by a coupling mated to the engine driven gear
assembly. The pump is mounted on the accessory section of the engine.