Piper COMANCHE PA-24-180 Service Manual page 661

NOTE
Do not attempt adjustment of this vtlve with the engine in operation.
b. Snrt the engine. After allowing time for wrm-up, mn the engine at medium RPM.
c. With the engine running at medium RPM. the uction gauge should indicate between 4.2 and 4.7
inches of mercury. Units with a cenrl
air filter yem
should indicate between 4.8 and 5.1 inches of
mercury. If the vacuum reading fails to fall within this rmge, shut down the engine and adjust the regulator
valve. Move the valve adjustmen srew dockwise to incree te presure and counterclockwise to e
se
the presmre Start the engine and repeat the cheek.
d After the ynsem presure has been adjusted o the recommended sttings. reuighten the locking
mut or replace the protective cap.
11-14. Vacuum Pump. 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
11-15. Vacuum Pump Removal The vacuum pump i 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 fittngs. Identify
the hoses to aid in reinaullron.
c. Remove the four retaining nuts lock washers and plain washers.
d. Remove the vacuum pump.
NOTE
Before inulaaion of firting on pump, check for aernal damge. A
pump that has been damaged or dropped should not be istalled. When
a vise is used to secure pump while insalling fiings. suitable caution
murt be exercised to avoid pump damage. The square moaunng flange
must be held berween soft wood blocks and only at righ angles to the
vise jaws Use only enough vise presure to hold pump firmlv. DO NOT
apply vue presure to outside diameter or overall length. The port of
the AIRBORNE dry air pump have been treated with a dry film
lubricant and the AIRBORNE fitings
ae cadmium plated thus
eliminatng any need for thread lubricnts. If a thread lubricant is
required use a powdered moly sulfide or grphite in dry form or in an
evaporaing vehicle; or employ a ilicone spray. Apply sparingy to
external threads of firings only. DO NOT use pipe tape, thread dope,
hydrocarbon oil or greaseu as hese can contaminate pump and cause
malfunction. With pump properly secured in vise, insert ficings in ports
and hand tghten firmly. Next, using a wrench. ightcn each fittng from
one-half to two turns addinonaL
INSTRUMENTS
REVISED: 4/10/81
3 F22
PIPER COMANCHE SERVICE MANUAL