SPOILER UP
OVERTRAVEL
PISTONS

ACTUATOR SNUBBER ROD AND CYLINDER CHECK VALVE PISTON
PRESSURE RETURN
PORT PORT

INPUT LEVER (EXTERNAL)
RETRACT EXTEND
Flight Spoiler Actuator Schematic Figure 7
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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C.
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737-300/400/500MAINTENANCE MANUAL
Hydraulic power to the flight spoiler power control units is controlled by spoiler shutoff valves in the flight controls hydraulic modular packages. Switches for these electrically-operated valves are located on the pilots' forward overhead panel. Hydraulic system A powers flight spoilers 3 and 6. Hydraulic system B powers flight spoilers 2 and 7.Each flight spoiler actuator quadrant is bracket mounted on the actuator support fitting and pivots on two sealed bearings. The quadrants have three cable grooves to receive wing spoiler cables. The quadrant crank is mounted on a boss around the quadrant hub and is secured in place by two shear rivets. A white painted scribe mark is provided to aid detection of shearout. Each actuator quadrant has a rigging pin hole.The flight spoiler actuator is connected to the quadrant by an actuator link. The input arm on the actuator is adjustable to provide proper spoiler pickup. The input arm has two mounting locations for the actuator link. The forward position is used for the flight spoilers.When the actuator is pressurized, the extension check valve is held open by pressure acting on a piston at the base of the valve (Fig. 7). If hydraulic pressure is lost, springs reseat the extension check valve to prevent spoiler float. A blow-down check valve located in the pressure line allows the spoilers to blow down at critical speed. Protection against actuator damage due to thermal expansion of entrapped hydraulic fluid or extreme "up" loads from the flaps is provided by a thermal relief valve and relief check valve. The thermal relief valve and the extension check valve are one unit; however, the thermal relief valve is opened by actuator down pressure operating an additional piston. The thermal relief valve is set to open when a pressure of 3000 to 3600 psi is reached with hydraulic power off, and to reseat at a pressure no lower than 2500 psi. The relief check valve will also protect against damage from extreme flap up loads when hydraulic power is on. To prevent hydraulic lock when the spoilers are in the full down position, a snubber check valve is built into the piston. With the spoilers retracted and the piston in the full "down" position, an "up" signal to the control valve allows hydraulic fluid to flow to the base of the cylinder, around the piston, and through the snubber check valve to the face of the piston. The thermostat valve provides a hydraulic bleed at low temperatures to maintain warm hydraulic fluid in the actuator.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500
MAINTENANCE MANUAL

FLIGHT SPOILER 
ACTUATOR (TYPICAL) 
1 
2 
HYDRAULIC  HYDRAULIC 
SYSTEM"A"  SYSTEM"B" 
PRESS  RET  RET  PRESS 
SPOILER 
SHUTTOFF  FLIGHT CONTROLS 
VALVE  SHUTOFF VALVE 
5  6  5  6 
3  7  3  7 
4  2  4  2 

FLT CONTROL STANDBY A B HYD LOW QUANTITY
STDBY STDBY RUD RUD LOW PRESSURE
OFF OFF
A ON B ON
ALTERNATE FLAPS OFF
UP PRESSURE
LOW
LOW
PRESSURE
OFF SPOILER A B ARM
DOWN
1
OFF OFF
FEEL DIFF PRESS
ON ON
2
SPEED TRIM FAIL
MACH TRIM YAW DAMPER FAIL
YAW
AUTO SLAT DAMPER
FAIL
OFF
ON
Flight Spoiler Hydraulic System Schematic
Figure 8

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