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737-300/400/500MAINTENANCE MANUAL
 HYDRAULIC POWER TRANSFER UNIT (PTU) SYSTEM - DESCRIPTION AND OPERATION
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General (Fig. 1)
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 A.  The power transfer unit (PTU) system provides an alternate power source for autoslat operation if system B EDP pressure is lost. This alternate power system applies to only the leading edge devices. The PTU uses system A pressure to drive system B fluid without transferring fluid between the two systems. The PTU contains in one integral assembly, a hydraulic motor and a hydraulic pump joined by a driveshaft.
 B.  An electric motor operated control valve opens to provide system A pressure to drive the motor. The motor drives the pump which uses system B fluid from the reservoir to provide pressure for extending leading edge devices between the retract and full extend positions.
 C.  A filter, hydraulic fuse, and check valve are placed in the pump pressure
 line to provide filtration, emergency shutoff, and back-flow control.Power Transfer Unit (PTU) (Fig. 1)
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 A.  The power transfer unit consists of a hydraulic motor and a hydraulic pump joined to an integral support housing. The motor and pump are joined by a driveshaft inside the housing. The hydraulic motor uses 9.8 gpm at 2400 psi (pounds per square inch differential) to provide a pump output of 6.5 gpm minimum at 2400 psi minimum. The PTU is mounted on the keelbeam forward of the standby reservoir in the center wheel well.
 B.  The hydraulic motor is a fixed displacement piston type. Fluid enters the motor through a flow limiter and a control valve. The flow limiter controls motor speed by limiting the fluid flow to the motor to about 12 gpm. The motor moves fluid through the motor case to lubricate and cool the motor. The case drain fluid flows into the A system return line.
 C.  The pump is an inline piston type with a fixed displacement. The pump moves fluid through the pump case to lubricate and cool the pump. On airplanes with a T-fitting downstream of the case drain filter for the B system electric motor driven pump, the PTU case drain fluid flows into the B system return line. On airplanes with an elbow in place of a T-fitting, the PTU case drain fluid flows to the case drain filter for the B system electric motor driven pump and then to the B system reservoir.
PTU Pressure Filter Module (Fig. 1)
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 A.  The PTU pressurized fluid is filtered upon entering the system B lines. The filter module is mounted forward of the PTU on the system B EMDP support structure in the right center wheel well. The filter has a disposable element. Hydraulic fuses and check valves are mounted downstream of the filter in the pressure line.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

737-300/400/500MAINTENANCE MANUAL
SEE B
LIMITER FLOW  PRESSURE SYSTEM A LINE  LINE RETURN SYSTEM A MOTOR PTU  PUMP PTU LINE CASE DRAIN PTU MOTOR  DRAIN LINE PTU PUMP CASE  SEE  A 
VALVE CONTROL PTU  EDGE DEVICES TO LEADING SUPPLY LINE SYSTEM B 
KEEL BEAM 
FILTER PTU PRESSURE 
UNIT (PTU) TRANSFER POWER 
A 
RESERVOIR SYSTEM B (REF) 

SYSTEM B PRESSURE MODULE (REF)
EDP, AUTO SLAT SYSTEM PRESSURE SWITCH
SYSTEM B RETURN FILTER (REF)
B
Power Transfer Unit (PTU) Components Figure 1
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL

TO SYSTEM A RETURN
LEGEND

PRESSURE

FILTER
SUPPLY
CHECK VALVE
RETURN

HYDRAULIC FUSE

Power Transfer Unit (PTU) Schematic
Figure 2 (Sheet 1)

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