757 AMM 飞机维护手册 液压 CHAPTER 29 - HYDRAULIC POWER 2(121)

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 D. PTU Control Valve (Fig. 4)
 (1)  The control valve is a shutoff valve in the PTU motor supply line. The valve is on the inboard wall of the right wheel well. The two-position valve is operated by a 28 volt dc motor. In the ON position, the valve supplies right system pressure to operate the hydraulic motor. In the OFF position, the valve shuts off pressure to the motor.
HYDRAULIC 
LINE 
(2 PLACES)  PTU CASE DRAIN 
FILTER MODULE  CHECK 
INDICATION  VALVE 
PRESSURE 
SWITCH 
CHECK VALVE  HYDRAULIC 
LINE 
PTU PRESSURE  (2 PLACES)  DIFFERENTIAL 
FILTER MODULE  PRESSURE 
INDICATOR 
CONTROL 
DIFFERENTIAL  PRESSURE 
PRESSURE  SWITCH 
INDICATOR  FILTER 
FILTER 

PTU CASE DRAIN FILTER MODULE
PTU Filter Modules
Figure 3

PTU PRESSURE FILTER
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MAINTENANCE MANUAL

 E. Left EDP Pressure Switch
 (1)  The left EDP pressure switch, which controls left EDP low pressure indication, also turns on the PTU if left EDP pressure drops below approximately 1275 psi. (Ref 29-11-00 for EDP pressure switch location and more information.)
 3. Operation
_________
 A. Functional Description (Fig. 5)
 (1)  Automatic Operation
 (a)  In automatic (normal) operation, 28 volt dc power is provided through the PTU manual switch OFF position to the left engine-out relay No. 2. This relay closes if power is lost in the left engine. If the right engine is still running, power is routed to the PTU control valve through the right engine-out relay No. 4 and the PTU ON relay. If the left engine is running, but the left EDP pressure drops below approximately 1275 psi, 28 volt dc power is routed through the left EDP pressure switch, right engine-out relay NO. 4, and PTU ON relay to the PTU control valve. The valve motor drives the PTU control valve to the open position. This supplies right system pressure to operate the PTU hydraulic motor which drives the pump.
HYDRAULIC LINE

VALVE POSITION INDICATOR AND MANUAL OVERRIDE ARM
VALVE VALVE
ACTUATOR MOTOR
PTU Control Valve
Figure 4

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COMPUTER TO LEFT SUPPLY
HYDRAULIC
SYSTEM
RETURN
Power Transfer Unit System Schematic
Figure 5

28V DCL BUS

P11
LEGEND

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(b)
　
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