(6)
Connect the sense lines (3 locations).
S 424-028
(7)
Attach the regulator to the engine bracket with the bolts, washers and nut.
S 434-022
NOTE:____The nut goes at the top aft bolt hole. There are nutplates at the remaining bolt holes. The chamfer of the washers is in the direction of the bolt heads.
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737-300/400/500MAINTENANCE MANUAL
S 714-029
(8) Do the test for the high stage regulator:
NOTE: The following test requires an engine run to check the
____ duct pressure. You may also use the High Stage Valve and High Stage Regulator - Adjustment/Test (AMM 36-11-85/501) procedure. This Adjustment/Test procedure uses a nitrogen source to check the operation of the high stage valve and regulator.
(a)
Remove the DO-NOT-OPERATE tags from the components that follow: 1) The BLEED switch 2) The start lever. 3) The forward thrust lever.
(b)
Remove the DO-NOT-CLOSE tag and close the circuit breaker for the bleed air control.
(c)
Use the engine to pressurize the pneumatic system (AMM 36-05-00/201).
NOTE: Do not use more than the idle power of the engine.
____
(d) Examine the connections for leakage.
NOTE: There is no leakage permitted.
____
(e)
Close the right fan cowl panel (AMM 71-11-02/201).
(f)
Do the Bleed Air Control System Operational Test - Engine (AMM 36-11-05/501, step 5.).
E. Put the Airplane To Its Usual Condition
S 864-031
(1)
Supply pressure to the pneumatic system (AMM 36-05-00/201).
S 444-032
(2)
Do the activation procedure for the thrust reverser
(AMM 78-31-00/201).
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737-300/400/500MAINTENANCE MANUAL
BLEED AIR PRECOOLER SYSTEM - DESCRIPTION AND OPERATION
______________________________________________________
1. General_______
A. The purpose of the bleed air precooler system is to control the temperature of the high pressure bleed air which is supplied to the manifold system to approximately 415°F. Two precooler systems are provided, one for engine No. 1 and one for engine No. 2. Each precooler system consists of an air-to-air heat exchanger, four-inch-diameter precooler control valve, a precooler control valve sensor and a solenoid valve installed in the sense line between the valve and sensor.
2. Precooler (Fig. 2)_________
A. The precooler is an air-to-air heat exchanger located at top right center of each engine and is of the plate-fin single pass crossflow type. The heat collected from the hot air ducted from the engine is absorbed by the cool air ducted from the engine fan after passing through the precooler control valve. The cooling air is then discharged overboard.
3. Precooler Control Valve (Fig. 2 and 3)_______________________
A. The precooler valve is attached to the discharge port of the engine fan (Ref Fig. 2). The purpose of the valve is to control the flow of cooling air through the heat exchanger to regulate the temperature of the bleed air. This is a pneumatically actuated, temperature controlled, spring loaded open butterfly modulating valve. A remote pneumatic temperature sensor is used to produce a valve position that is proportional to the sensed temperature. The valve is closed at low sensed temperature and open at high sensed temperatures. Supply pressure from the pneumatic manifold is applied to the supply port on the valve. This pressure is ported to the base of two reference pressure regulators. Supply air flows through the reference pressure regulator metering valve and through an orifice to Chamber "A". When the sensed pressure reaches the desired level, the spring force is overcome and the metering valve moves toward the seat to maintain the outlet pressure at a constant level. The regulated outlet pressure from the actuator reference pressure regulator is routed through Orifice "A" to a control nozzle and butterfly actuator. The regulated outlet pressure from the servo reference pressure regulator is routed through a valve driven feedback control orifice to the remote temperature sensor and to the servo. The remote temperature sensor functions as a variable orifice producing a control pressure in servo Chamber "B" that is inversely proportional to sensed temperature thereby driving Chamber "B" pressure up with decreasing temperature and down with increasing temperature. When the remote temperature sensor is closed, Chamber "B" pressure is at its maximum, the control nozzle is closed by the pressure force on Diaphrgm "B" and the actuator pressure is at its maximum value which is sufficient to overcome the valve opening spring and drive the butterfly fully closed. A decrease in servo Chamber "B" pressure permits the load of the servo spring to pull the lever away from the control nozzle which produces a decrease in the actuator chamber pressure. As the actuator pressure decreases, the actuator opening spring force strokes the butterfly in the opening direction until a force balance exists between actuator and spring force. As the butterfly strokes toward the opening direction, the feedback spring produces an increasing tension load on the lever.
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