(c)

(d)

(e)

(f)

(g)

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MAINTENANCE MANUAL

Fluid is supplied to the PTU pump from the reserve supply outlet on the left system reservoir. The reserve supply outlet draws fluid from the bottom of the reservoir to allow use of a reserve amount of fluid retained there for use only by the PTU pump, by a standpipe on the EDP and ACMP supply outlet.The PTU pump is normally supplied fluid from the left system reservoir. However, if reservoir pressure and fluid level are low, fluid could be trapped in the reservoir. If this happens, the PTU pump can take fluid directly from the left system return line, bypassing the reservoir. A hydraulic line and check valve connects the PTU pump supply line to the left system return line at the reservoir for this purpose.The pump output flows through a filter in the PTU module before entering the left system. Fluid flows through the pump case for cooling and lubrication. This case drain fluid is filtered by the PTU case drain filter before returning to the left system.If the PTU pump does not supply at least 400 psi within three seconds, the PTU control pressure switch will actuate the PTU on relay. This closes the PTU control valve to remove right system pressure from the PTU and stop the motor.The PTU indication circuit will supply a ground signal to the EICAS computers if the PTU system does not operate properly. This signal causes a POWER XFER UNIT message to be displayed in the EICAS status and maintenance modes.The PTU indication circuit supplies a ground signal to EICAS under the following conditions: 1) PTU pump output less than 400 psi with the right engine
 running and the left engine not running or the left EDP pressure below 1275 psi. 2) PTU pump output more than 400 psi with the left engine running and the left EDP pressure above 1275 psi.
 3)  PTU pump output more than 400 psi with the right engine not running and the left engine not running or the left EDP pressure below 1275 psi.
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MAINTENANCE MANUAL

 (2)  Manual Operation
 (a)  
In manual operation, 28 volt dc power is provided to the PTU manual switch. The PTU can be operated by moving the manual switch on the right side panel P61 to the ON position. This provides power to the PTU control valve by-passing the left and right engine-run/out logic and the left EDP pressure switch. The valve then opens to operate the PTU the same as automatic operation.

 (b)  
The manual switch is moved to the OFF position to shut off the PTU. This provides power to reverse the PTU control valve motor and close the valve. With the valve closed, right system pressure is removed from the PTU motor.

 (c)  
In manual operation, the POWER XFER UNIT message will be displayed on EICAS if the PTU pump output is less than 400 psi.

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FAULT ISOLATION/MAINT MANUAL

HYDRAULIC POWER TRANSFER UNIT (PTU) SYSTEM
COMPONENT  SHT 102 FIG.  QTY  ACCESS/AREA  REFERENCE 
CIRCUIT BREAKER  1  FLIGHT COMPARTMENT, P11 PANEL 
　
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