Vacuum Pressure Adjustment


Subject: Vacuum Pressure Adjustment/Test (For airplanes with the Parker Airborne regulator valve or the Aero Accessories regulator valve)
NOTE: Before the adjustment procedure, the entire pneumatic system must be inspected and tested for leaks, restrictions, and unserviceable components. Failure to correct all system anomalies will lead to reduced dry air pump service life.
A. Prepare the System for the Test.
(1) Remove the gyro (central air) filter.
B. Do a Check of the Regulator Valve.

CAUTION: Make sure that the temperature of the engine does not go above the
maximum engine temperature during the adjustment/test of the regulator valve.
NOTE: At engine speeds between 1200 RPM and full throttle, suction must fall between 4.5 in.hg. and 5.5 in.hg. (Green range on gage).
(1) Start the engine, warm up to the normal operating temperature, and run at static RPM. Refer to Pilot's Operating Handbook and FAA Approved Airplane Flight Manual.
(2) Make sure the suction gage indication does not go above 5.5 in.hg.
(3) Run the engine at 1200 RPM and make sure the gage indication does not go below 4.5 in.hg.
(4) If the suction indication falls outside of the range, shut down the engine and adjust the regulator valve in the steps that follow.
(a) Bend the locking tab upward on the lower surface of the regulator valve.
CAUTION: Be careful when you turn the adjustment screw. Do not turn
it too much in either direction. When you turn it too much in either direction, damage can occur to the equipment.
(b) Turn the adjustment screw on the lower surface of the regulator valve in the direction to increase or decrease the pressure as necessary.
NOTE: As you face the adjustment screw, when you turn it clockwise the pressure
increases. When you turn it counterclockwise, the pressure decreases.  
 (c) Tap the regulator after you adjust it to help reset the components.
(d) Bend the locking tab downward to keep the adjustment screw in place when the correct pressure has been set.
(5) Run the engine at static RPM and make sure the gage indication does not go above 5.5 in.hg.
(6) Run the engine at 1200 RPM and make sure the gage indication does not go below 4.5 in.hg.
(7) Shut down the engine.
(a) For airplanes without the Garmin G1000, make sure that the L VAC R lights come on.
(b) For airplanes with the Garmin G1000, make sure that the low vacuum annunciator visual and aural warnings come on.
(8) Attach the filter element to the gyro (central air) filter.
(9) Before you start the engine, make sure that the low vacuum annunciations are on.
(a) For airplanes without the Garmin G1000, make sure that the L VAC R lights are on.
(b) For airplanes with the Garmin G1000, make sure that the low vacuum annunciator visual warning is on.
(10) Run the engine for a final time at static RPM and observe the indication on the suction gage.
(a) If the indication falls noticeably after the filter is installed, replace the filter.
(11) Reduce the engine speed to 1200 RPM and make sure that the suction stays in the green range (does not fall below 4.5 in.hg.)and that the low vacuum annunciations are off.
(a) For airplanes without the Garmin G1000, make sure that the L VAC R lights go off.
(b) For airplanes with the Garmin G1000, make sure that the low vacuum annunciator visual and aural warnings  
 (12) Shut down the engine.
Reference Cessna MM Rev.18

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