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5. Vacuum Regulator:
A. The vacuum regulating valve seldom needs replacement. Symptoms that suggest replacement are:
(1). Chatter as indicated by rapid fluctuation of the vacuum gauge needle or an audible sound. (2). Non-repeatability of the vacuum gauge reading when the panel gauge is not suspect or has been checked against a known test gauge (cruise RPM only).
B.  Regulator malfunction tends to increase the vacuum power applied to the gyros. Thus, although excess vacuum is applied, a loss of vacuum does not occur.
C.  The gyros themselves act as a limiting device to keep the vacuum power applied from exceeding safe levels.
— Note —
If the panel gauge has been checked and found OK and the vacuum gauge reading does not repeat within the range of 5.0 ± .2 inches of mercury then the regulating valve should be changed. Observe the usual precautions for maintaining system cleanliness to avoid premature pump service.
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TROUBLESHOOTING.
A Troubleshooting Chart is provided to assist in locating and correcting possible malfunctions in the system.
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CHART 3701. TROUBLESHOOTING (VACUUM SYSTEM)

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CHART 3701. TROUBLESHOOTING (VACUUM SYSTEM) (cont)
Trouble  Cause  Remedy 
No vacuum gauge indi-cation at instrument.  Filter clogged or dirty. Line from gyros to filter restricted or leaking.  Clean or replace filter. Check line. 
No vacuum gauge indi-cation at instrument.  Faulty gauge or mal-functioning pump.  Replace gauge. Replace pump. 
Low vacuum system pressure.  Filter dirty. Vacuum regulator valve incorrectly adjusted. Line from gyro to filter restricted or leaking. Line from pump to manifold leaking.  Clean or replace filter. Adjust regulator valve in accordance with adjustments in this section. Repair line. Check all lines and fittings. 

Figure 37-2. Vacuum Regulator 
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2L12 

DISTRIBUTION.
VACUUM REGULATOR VALVE.

Two vacuum regulator valves that contain filters are incorporated in the system to control vacuum pressure to the gyro instruments. A manifold check valve assembly assures vacuum if one engine or pump should fail.
ADJUSTMENTS TO VACUUM REGULATOR VALVE. (Refer to Figure 37-2.)
1.  
Remove nacelle cover(s), straighten adjustment screw lock tabs on valve.

2.  
Adjust regulator screw in accordance with the direction desired, run engine to check results.

— Note —
With one engine operating at 2000 RPM and the opposite engine at idle or off, set the vacuum regulator at 5.0 ± .2 inches of mercury. Repeat for opposite engine. After adjusting regulators check vacuum is within limits with both engines at 2000 RPM.
3.  When the recommended vacuum indications are attained, bend tabs to lock adjusting screw, restore aircraft to airworthy condition.
REMOVAL AND REPLACEMENT OF REGULATOR VALVE.
1.  
To remove the regulator valve, disconnect the two lines, remove the mounting nut and remove the valve.

2.  
Replaced regulator in reverse order given for removal. Check complete vacuum system for proper option.

VACUUM PUMP.
The vacuum pump is of the rotary vane, positive displacement dry type. This 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 means of a coupling mated to the engine driven gear assembly. A pump is mounted on the accessory section of each engine. The pumps differ to account for engine rotation, the starboard engine utilizes a clockwise pump, the port engine utilizes a counter clockwise pump.
REMOVAL AND INSTALLATION OF VACUUM PUMP.
1.  
Remove the top portion of the engine cowling.

2.  
Disconnect the two hoses at the pump.

3.  
Remove the four mounting nuts, lockwashers and plain washers, and withdraw the pump from the engine.

— CAUTION —
THE ONLY DRY AIR PUMP MOUNTING GASKET AUTHORIZED AND APPROVED FOR USE ON AIRBORNE DRY AIR PUMP IS THE AIRBORNE GASKET B3-1-2, PIPER PA RT NUMBER 751 859.  USE OF ANY OTHER GASKET MAY RESULT IN OIL SEEPAGE OR LEAKAGE AT THE MOUNTING SURFACE. TORQUE THE FOUR MOUNTING NUTS TO 50 - 70 INCH-POUNDS.
4.  
Reinstall the pump in reverse order of removal.

5.  
Install the fittings with a torque of 95 to 110 inch-pounds.

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