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 4.  Leading Edge Slat Aerodynamic Seal
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 A.  During leading edge slat extension, wing leading edge aerodynamic seals prevent airflow through cutouts provided in wing fixed leading edge skin for attachment, actuation, and heating of leading edge slats.
 5.  Leading Edge Flap and Slat Control Valve
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 A.  A three-position control valve regulates operation of the leading edge flaps and slats (Fig. 1). The control valve is mounted on the trailing edge flap follow-up mechanism located in the right wheel well. The valve consists of a sliding piston enclosed in a valve housing. Drilled passages are provided in the valve housing for a pressure port, a return port, and two cylinder ports. A pushrod connects the control valve to the trailing edge flap follow-up mechanism. With the trailing edge flaps retracted, the control valve slide blocks pressure to the leading edge flap and slat actuator extend ports. When the trailing edge flaps extend to the 1- to 5-unit position, pressurized fluid is ported through one of the cylinder ports to extend the leading edge flaps and to extend the leading edge slats to the intermediate position. When the trailing edge flaps reach the 10-unit position, pressurized fluid is ported through both control valve cylinder ports to fully extend all leading edge slats.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

737-300/400/500
MAINTENANCE MANUAL

STANDBY PRESSURE  SYSTEM B PRESSURE  EXTEND PRESSURE FROM CONTROL VALVE 
STANDBY SYSTEM BLOCKING VALVE  FILTER 
SYSTEM B BLOCKING VALVE 
VENT 

SYSTEM B PRESSURE STANDBY PRESSURE EXTEND PRESSURE
Leading Edge Flap Actuator
Figure 2

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 ALL  ú ú 01 Page 8 ú Oct 20/83
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
T81376
A 737-300/400/500MAINTENANCE MANUAL
 6.  Leading Edge Flap Actuator
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 A.  A two-position hydraulic actuator mounted on the front spar of the wing is used to extend and retract each leading edge flap (Fig. 2). A self-aligning bearing at each end of the actuator allows the actuator to rotate about mounting bolts. The actuator housing contains two blocking valves and a piston and rod assembly. The blocking valves will hydraulically lock the actuator pistons in position if hydraulic pressure drops below 2000 psi. If a loss of pressure occurs, a compression spring moves the blocking valve slide to prevent flow of hydraulic fluid through the valve. One blocking valve is used for hydraulic system B while the second blocking valve is used for the standby hydraulic system.
 B.  External ports in the actuator housing are provided for an actuator retract pressure line, an actuator extend pressure line, and a standby system pressure line. The actuator retract pressure is provided by B system pressure. With the hydraulic system pressurized, system B pressure is ported at all times to the retract side of the actuator piston. System B hydraulic pressure from the control valve extends the actuator by acting upon a larger piston area than the pressure attempting to retract it. When the control valve is closed, the extend side of the piston is ported to return. The flap will then retract due to hydraulic system B pressure on the retract side of the piston.
 C.  During standby hydraulic system extension, the standby blocking valve is opened by standby pressure to pressurize both extend and retract sides of piston. A restrictor in the valve passage controls flow to the actuator. Standby pressure is also applied to close valve preventing loss of fluid to normal system. Standby pressure is also applied to close the B system blocking valve preventing loss of fluid to normal system. The actuator will remain in the fully extended position until system B hydraulic pressure is restored.
 7.  Leading Edge Slat Actuator (Fig. 3)
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 A.  A three-position hydraulic actuator mounted on the front spar of the wing is used to extend and retract leading edge slats 1 thru 6. The three actuator positions are retracted, intermediate extension, and full extension. Each actuator housing contains two blocking valves, an internal mechanical locking mechanism, an outer piston, and an inner piston and rod assembly. The actuator outer piston slides within the actuator housing and the inner piston slides within the outer piston. The internal mechanical locking mechanism consists of a spring-loaded piston and locking segments. The mechanism locks the actuator in the retracted position in the absence of extend pressure. When extend pressure is applied, the locking piston moves against spring force to retract the locking segments and allow the actuator to extend. The blocking valves hydraulically lock the actuator pistons in position if hydraulic pressure drops below 2000 psi. If a loss of pressure occurs, a compression spring moves the blocking valve slide to prevent flow of hydraulic fluid through the valve. One blocking valve is used for hydraulic system B while the second blocking valve is used for the standby hydraulic system.
　
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