ENGINE EXHAUST PRESSURE PROBE AND MANIFOLD - INSPECTION/CHECK
1. General
A. Engine compartment cleanliness is important because the extensive mass airflow tends to draw foreign objects into the engine. Thoroughly clean the entire engine compartment with a vacuum cleaner after completion of any work. Keep the compartment and the annular duct free of dirt, oil and grease, and remove all unused parts, such as nuts, washers, and pieces of lockwire. Immediately cover all apertures resulting from the disconnection of tubing or parts. Use external caps on all tube openings, not internal plugs.
B. Carefully check the engine exhaust gas pressure probes and manifold without dismantling to ensure that all connections are tight and free from leaks and that lines, and tubing are secure.
C. Check engine exhaust (discharge) pressure probe for burned or broken probe and for security of probe and attached line.
NOTE: If one of the Pt7 manifold tubes has a crack or a leak, you can disconnect and remove that tube. The Pt7 probe fitting (on both ends of the removed manifold tube) must be sealed off with a stainless steel cap and safety wired. This procedure is limited to one Pt7 manifold tube and must be used for temporary engine operation only. Test the engine and do a check for the correct EPR limits. Replace the defective Pt7 manifold tube with a new or repaired tube as soon as possible.
2. Engine Exhaust Pressure Probe and Manifold Check
A. Prepare Engine Exhaust Pressure Probe and Manifold for Leakage Check
(1)
Check that thrust reverser is in forward thrust position to permit entrance into engine exhaust section.
(2)
Observe the following precautions for maintenance in engine exhaust section:
(a)
Pull (open) applicable engine START IGNITION circuit breaker on circuit breaker panel P6-2, and placard the circuit breaker with DO NOT CLOSE.
(b)
Placard thrust reverser controls with DO NOT OPERATE.
WARNING: SERIOUS INJURY CAN OCCUR IF ENGINE IS STARTED AND/OR IF THRUST REVERSER IS OPERATED.
(3)
Enter engine exhaust section.
(4)
Tape all exhaust pressure (Pt7) probe inlet ports.
(5)
Obtain access to exhaust pressure line connection on engine by opening left cowl panel. Refer to Chapter 71, Power Plant.
(6)
Disconnect exhaust pressure line from exhaust pressure manifold outlet elbow. For location, refer to 77-11-0, figure 501.
(7)
Connect air hose to exhaust pressure manifold outlet elbow.
NOTE: Forward row of probes are exhaust pressure probes. Rear row of probes are EGT probes.
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Jun 20/90 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 77-11-31 Page 601
B. Check Engine Exhaust Pressure Probe and Manifold for Leakage
(1)
Pressurize manifold to 20 psi and listen for leakage within fan air duct. If leakage is detected, make repairs with assistance of local P&WA representative.
(2)
Relieve test pressure in manifold.
(3)
Disconnect air hose from manifold outlet elbow.
(4)
Reconnect exhaust pressure line.
C. Restore Airplane to Normal Configuration
(1)
Remove tape from exhaust pressure probes.
(2)
Close engine cowl panel.
(3)
Remove placards in control cabin.
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ENGINE TACHOMETER SYSTEM - DESCRIPTION AND OPERATION
1. General
A. The engine tachometer system measures the rotary speed of an engine low pressure or high-pressure compressor rotor and provides visual speed indication to the pilots for monitoring engine performance. The engine tachometer system consists of two generator units (N1 and N2) on each engine and corresponding tachometer indicators on the center instrument panel. The N1 tachometer indicator shows the speed of rotation of the low-pressure compressor. The N2 tachometer indicator shows the speed of rotation of the high-pressure compressor. (Fig. 1)
B. The tachometer generators, driven by the compressor rotors through reduction gearing, generates alternating electrical signals. The electrical signals, received from the generators, energize corresponding indicators, which in turn show their respective compressor speeds in percent. A test receptacle, used to attach a master indicator, is included in the circuit to provide a means of checking the system.
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