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C. The steering metering valve incorporates a spring compensator to maintain a pressure of 70 to 130 psi against the actuator pistons to act as a shimmy damper. The valve structure includes two bypass check valves to allow flow of hydraulic fluid between each set of ports to prevent cavitation. A bypass valve protects the steering system from high pressures developed in the steering cylinders during towing. With the steering hydraulic system depressurized, residual pressure, coupled with small frictional forces within the valve, act to retain the bypass valve in the closed position (Fig. 1). When the nose gear is turned by the towing vehicle, the steering actuator pistons act like pumps, forcing fluid out of the steering cylinders and creating a pressure differential across the bypass valve. The valve opens allowing equalizing pressure to act against the actuator pistons in opposition to the turning force supplied by the towing vehicle. The net result is that pressure is equalized on the opposing sides of the steering actuator pistons. The bypass valve is held in the closed position whenever the steering hydraulic system is pressurized.
D. Towing may also be accomplished without depressurizing hydraulic system A by actuation of the manually operated steering depressurization valve. Depressing valve plunger and installing ground lock pin depressurize the steering valve by blocking pressure and connecting steering valve pressure port to return. After towing is completed and tow bar disconnected, pulling ground lock pin will allow valve to open to repressurize steering valve.
3. Nose Gear Steering Collar_________________________
A. The nose gear steering collar is held clamped around the outer cylinder in an annular recess immediately below the trunnions (Fig. 1). Both of the two steering cylinders are connected to the steering collar and the upper end of the upper torsion link is also connected to the steering collar. When force is applied to the steering collar, by either steering cylinder, the collar transfers the force through the torsion links to turn the inner cylinder to the right or left respectively to which cylinder force is applied to give steering action to the nose wheels.
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32-51-00
ALL ú ú 01 Page 2 ú Oct 25/84
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
TRUNNION
HOLE RIG PIN PIN RIG SWIVEL FITTING
NWSA
CABLE NWSB
NGPPA NWSB
CABLE NWSA
SWIVEL VALVE STEERINGNGPPB SEE A
COLLAR METERING VALVE STEERING
RIG PIN STEERING TORSION
WHEEL SEE B LINKS
SWIVEL VALVE
FWD STEERING ACTUATOR
A
NOSE WHEEL STEERING SELECT SWITCH
1
CAPTAIN'S FORWARD PANEL
ROTARY ACTUATOR
CABLE NGPPA CABLEQUADRANT NWSA
RIG PIN HOLE
CABLE NGPPB
FWD CONTROL ROD (CONTROLLED SHEAR OUT)
RUDDER PEDAL STEERING MECHANISM
B
1
NOT ON ALL AIRPLANES
Nose Wheel Steering System Component Location Figure 1
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32-51-00
ALL ú ú 02 Page 3 ú Mar 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
STEERING
METERING CABLES
VALVE PISTON
SNUB COMPENSATOR
(70 TO 130 PSI) STEERING METERING
VALVE
RETURN VALVE
RESTRICTOR
CENTERING
SPRING
BYPASS VALVE 1 2 3 4
STEERING METERING VALVE CRANK VALVE DEPRESSURIZATION STEERING
STEERING ACTUATORS FILTER FITTINGS SWIVEL
LINE GEAR DOWN LANDING VALVE CHECK
SWIVEL VALVES ACTUATORS TO LANDING GEAR LINE GEAR UP LANDING
STEERING COLLAR SELECTOR VALVE LANDING GEAR R C1 P C2 PRESSURE SYSTEM RETURN
LEGEND
SYSTEM PRESSURE SNUB COMPENSATOR PRESSURE
RETURN
Nose Wheel steering Schematic Figure 2 (Sheet 1)
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