37 VACUUM

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TTP
B1-L3
ATA 37
Beech 90 Series
B2-L2
Vacuum 
 
Vacuum system has a filter, vacuum gage, vacuum instruments, regulator valve, vacuum manifold, low vacuum annunciator switches, engine-driven vacuum pumps and related plumbing.
 DESCRIPTION AND OPERATION                                                                                          The vacuum system furnishes vacuum to operate the surface deice system, the instruments, the air-operated turn and slip indicator (if installed),the vacuum (gyro suction) gauge, and the cabin pressurization control system. To produce the vacuum, pneumatic air is passed through the ejector venturi. This draws air from the vacuum system regulator valve, the instrument air filter,the cabin pressure controller, and the cabin safety valve. Each of the components has filtered inlets that require periodic servicing.                                                                                            A vacuum regulator valve is in the avionics bay on the lower left corner of the forward pressure bulkhead, below the brake reservoir. The valve regulates filtered ambient air into the system to maintain sufficient vacuum (5.9 in Hg.) for proper operation of the vacuum-operated systems and components. The gyro suction gauge is on the copilot outboard subpanel.                                The instrument air filter is on the upper center of the forward pressure bulkhead, and is connected to the copilot attitude gyro and air-operated turn-and-slip indicator (if installed).The surface deicer system uses vacuum to deflate the deicer boots after inflation by pneumatic pressure and to keep the boots deflated.

 RUDDER BOOST SYSTEM

DESCRIPTION AND OPERATION

To prevent yaw caused by asymmetrical thrust ifan engine fails during a critical phase of flight, apneumaticallyoperatedrudderboostsystemauto-matically deflects the rudder toward the operating engine to decrease the yaw. Whenthe bleed air pressure from one engine drops 50psi below the bleed-air pressure from the oppo-site engine, the 50 psi differential pressure switchactuates the appropriate solenoid valve, allowingpressure from the pneumatic system manifold to actuate the rudder boostservoon the oppositeside.

Thesystemconsistsof:

•     Twopneumaticrudderservos

•     13-psipressureregulator

•     Twoventedsolenoidvalves

•     Inlineairfilterontheaftsideofthepres-sure bulkhead

•     50-psiddifferentialpressureswitchjustupstreamofthepneumaticmanifold

 

Each rudder boost servo is connected to the pri-mary rudder control cable through a bridle-cableassembly.Onlyoneservooperateswhentherudderbooster system is activated. The system is armedby a switch on the cockpit center pedestal from a5-ampcircuitbreakeronthecopilot CBpanel.




PTP 

Beech 90 Series

B1

LOC

FOT

R/I

MEL

TS

B2




371001 Vacuum System - Inspect for condition and security. B 05-12-02 120
371002 Vacuum Pumps - Check for condition and security. Check vacuum system breather

line for obstructions, condition, and security
371003 Vacuum System Hoses - Inspect for hardness, deterioration, looseness, or collapsed hoses. B 05-12-02 120
371004 Gyro Filter - Inspect for damage, deterioration and contamination. 
371006 Vacuum Manifold Check Valve - Complete a check for proper operation. (Only airplanes with dual vacuum pumps and Airborne manifolds.
371007 Do an inspection of the wear indicator ports on the vacuum pump described in the Tempest Service Letter 004.

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