75-24-00
 ALL  ú ú N03 Page 8 ú Feb 10/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
13. TVBCA Valve and TVCA Valve Solenoids (With Phase 3, Fig. 1)
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 A.  The solenoids are electrically operated, single coil, pneumatic type solenoid valves that supply pneumatic servo pressure to operate the TVBCA and TVCA valves.
 B.  The left solenoid controls the left TVBCA valve and the TVCA valve on the right side. The right solenoid controls the right TVBCA valve (and the IDG Air/Oil Heat Exchanger valve). The solenoids are installed on the aft face of the intermediate case at the 10 and 1:00 o'clock positions.
 C.  The solenoids are fail-safe to stop pneumatic servo pressure to the two valves which cause the shutoff valves to open.
 14. PS3 Air Filter (Fig. 1)
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 A.  ENGINES WITHOUT PHASE 3; The PS3 air filter (TVBCA filter) cleans muscle air (servo pressure) from the TVBCA valve solenoid before it goes to the TVBCA valves.
 B.  ENGINES WITH PHASE 3; The PS3 air filters clean muscle air (servo pressure) to the left and right solenoids and from the solenoids to the TVCA valve and right TVBCA valve.
 C.  The PS3 air filter is installed to a bracket on flange J of the HPC case at the 11 o'clock position.
 D.  The PS3 air filter assembly includes a filter head, element, and case. A poppet type bypass valve, in part with the filter head, opens at a differential pressure of 5 psid (34.3 kPad) and bleeds muscle air.
 E.  For more information on the PS3 air filter, refer to HPC Secondary Flow Control System (AMM 75-33-00/001).
 15. TVBCA Valve Position Switch (Engines Without Phase 3, Fig. 1)
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 A.  The position switch for the TVBCA valve gives visual and electrical indications of the open/closed condition of the right TVBCA valve.
 B.  The position switch, installed on the right TVBCA valve, includes an electrical connector, a switch, and a visual indicator.
 C.  When the TVBCA valve opens, the position switch assembly supplies a contact closure and applies a mechanical force against the switch linkage which causes the visual indicator pin to extend above the surface body. When the TVBCA valve is closed, the position switch supplies the EEC with an electrical position feedback signal.
 16. Turbine Vane Cooling Air Duct (Fig. 1)
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 A.  Four ducts for the turbine vane cooling air supply cooling air from the 12th-stage HPC to the 2nd-stage HPT vanes. The cooling air flows continuously through two of the air ducts, while cooling air through the two remaining air ducts is controlled by the TVBCA valves. Thus, 50 percent of the vane cooling air can be shut off at low power to get a higher engine efficiency.
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 75-24-00
 ALL  ú ú N03 Page 9 ú Jun 18/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
B.  Two of the air ducts are connected between the HPC aft case and the HPT case, while the two remaining air ducts are connected between the TVBCA valve and the HPT case.
 17. Operation
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 A.  Functional Description (Fig. 2)
 (1)  
Turbine Case Cooling System

 (a)  
During high power, climb, and cruise operation, the EEC commands the TCC air valve actuator to operate, and pull the control cable for the TCC air valve forward.

 (b)  
The control cable for the TCC air valve transmits linear control motion from the actuator to the linkage between the shutoff valves for the HPT and LPT case cooling air. When the control cable is pulled forward, the idler arm turns and pulls the turnbuckle forward which opens the shutoff valve for the LPT case cooling air. The shutoff valve for the HPT case cooling air opens when the idler arm turns more and pushes the lever arm upward.

 (c)  
When the TCC air shutoff valve opens, fan discharge air flows from the air inlet duct to the TCC air collectors. Cooling air then goes into the TCC air tubes and is discharged on the turbine case through air holes in the TCC air tubes.

 (d)  
The LPT air valve is open during high power, climb, and cruise operation, while the HPT air valve is open only during climb, but not during the initial 1,500 feet (457 meters) of climb after takeoff, and cruise operation.
　
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