R **ON A/C 059-099, 102-149, 151-199, 201-299, 301-399, 401-499,
 B. Solenoid Valves
 **ON A/C ALL
 A solenoid-controlled 2/2-way valve is installed in the PTU supply line of each system (Green and Yellow). They operate together to keep the PTU operative or inoperative.
 When the solenoid valve is energized, the spool moves into the port to close the valve. When the solenoid is de-energized , the spool moves away from the port to open the valve.
 C. Isolation Coupling 3701GM
 (Ref. Fig. 006)

 **ON A/C 001-049, 051-058, 101-101,
 An isolation coupling is installed in the power transfer unit manifold (3013GM) of the Yellow hydraulic system. It is a quick-release coupling which seals automatically when it is disconnected. It also has a ratchet lock to keep it connected.
 D. Pushbutton Switch (P/BSW) 1802GL
 The PTU P/BSW 1802GL is on the HYD section of overhead panel 40VU. It lets the crew control the operation of the PTU. The P/BSW is usually set to AUTO. In this position no power goes to the two solenoid valves (1012GL and 3012GL). If the crew set the P/BSW to OFF, the two solenoid valves get a 28V supply and they close. At the same time, the OFF light in the P/BSW comes on. The P/BSW has a FAULT light which comes on when the hydraulic systems have certain faults.

R **ON A/C 059-099, 102-149, 151-199, 201-299, 301-399, 401-499,
 An isolation coupling is installed in the power transfer unit manifold (3015GM) of the Yellow hydraulic system. It is a quick-release coupling which seals automatically when it is disconnected. It also has a ratchet lock to keep it connected.

 Isolation Coupling Figure 006
 1EFF : 1 1R 1CES  ALL  1 11 1 29-23-00 Page 18 Aug 01/05

 D. Pushbutton Switch (P/BSW) 1802GL
 The PTU P/BSW 1802GL is on the HYD section of overhead panel 40VU. It lets the crew control the operation of the PTU. The P/BSW is usually set to AUTO. In this position no power goes to the two PTU solenoid valves. If the crew set the P/BSW to OFF, the two solenoid valves get a 28V supply and they close. At the same time, the OFF light in the P/BSW comes on. The P/BSW has a FAULT light which comes on when the hydraulic systems have certain faults.
 **ON A/C ALL
 6. Operation/Control and Indication________________________________ 
R  **ON A/C 001-049, 051-099, 101-149, 151-199, 201-299, 301-399,
 (Ref. Fig. 002) 
R  **ON A/C 401-499, 
R  (Ref. Fig. 002A) 
R  **ON A/C ALL
 A. Usual Flight Condition
 The usual flight condition is the PTU system "armed" (the P/BSW set to AUTO and both solenoid valves open) and the Green and Yellow hydraulic systems at the same pressure. Because the pressures of the two hydraulic systems are in 500 psi of each other, the PTU does not operate (transfer pressure).
 B. Transfer of Power
 The PTU automatically starts to operate when the pressure in one of the two hydraulic systems is approximately 500 psi more than the pressure in the other system.
 A difference of pressure between the two systems moves the PTU servo valve and the variable cam. This causes a change in the stroke of the variable displacement motor. When the pressure difference is approximately 500 psi the change is enough to make the PTU start.

 Depending on the direction of movement of the servo valve, the variable displacement unit operates as a pump or as a motor.
 If the Green system has less pressure than the Yellow system, the stroke increases to its maximum. The variable displacement (Yellow) unit operates as a motor and the fixed displacement (Green) unit operates as a pump.
 If the Yellow system has less pressure than the Green system the stroke decreases to its minimum. The variable and fixed displacement units then operate as a pump and a motor respectively.
 C. Indications and Fault Warnings (Ref. Fig. 007, 008)
 The subsequent PTU status symbols can show on the HYD page of the lower ECAM Display Unit:
 -
PTU status symbols displayed in green color (outline only), directed toward the Green system. The status symbol is not connected to the Green or Yellow system lines. Occurs during normal operation when the PTU P/BSW is in AUTO position. The PTU does not transfer pressure.

 -
PTU status symbols displayed in amber color (outline only), directed toward the Green system. The status symbol is not connected to the Green or Yellow system lines. Occurs when there is a PTU fault transmitted from the Flight Warning Computer (FWC) or when the PTU P/BSW is in the OFF position.

 -
PTU symbols displayed in solid green color, directed toward the Green system. The status symbol is connected to the Green and Yellow system lines. Occurs when there is a Green-engine pump low-pressure.
　
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