(2)
ON ENGINES WITHOUT CFMI SB 74-009; The Type 4 distribution system has button type contacts, spring loaded elastomeric white chamfered silicone seals and a two piece cooling shroud which is retained by a clamp at the spark igniter end of the ignition lead. A Type 4 spark igniter is threaded into an igniter bushing at the spark igniter boss on the combustion case.
(3)
ON ENGINES WITH CFMI SB 74-009; The Type 4 distribution system has button type contacts, spring loaded elastomeric blue symmetrical silicone seals and a two piece cooling shroud which is retained by a clamp at the spark igniter end of the ignition lead. A Type 4 spark igniter is threaded into an igniter bushing at the spark igniter boss on the combustion case.
2. Description
___________
A. Ignition Leads
(1) Type 3 and Type 4 ignition leads (Fig. 1) are constructed of silicone insulated wire. Each type has sealed flexible conduit having a copper inner braid and a nickel outer braid. The leads connect the spark igniter to the output connectors of the ignition exciters. The aft ends of the leads, from the 3 o'clock strut support bracket to the spark igniter, are cooled by booster discharge air passing through the lead conduit.
B. Spark Igniter
(1) The spark igniter (Fig. 1) consists of a body, washer electrode or pin electrode, tip electrode, connector pin or contacts and ceramic insulation. There are 2 spark igniters in bosses at the 4 and 8 o'clock position on the combustion case. The tips of the spark igniters extend through ferrules in the outer liner into the combustion chamber. The depth of the spark igniter into the combustion chamber is controlled on the new Type 4 (SB 72-458).
3. Operation
_________
A. When the ignition exciter discharges the high voltage pulses through the ignition lead to the spark igniter, electric arc pulses occur between the electrode tip and ground washer or pin electrodes, and an ionized discharge occurs from the hole in the shell into the combustion chamber. The hot ion discharge ignites the fuel injected by the fuel flow nozzle. The electrical pulse discharges continue until electrical supply to the ignition exciter is discontinued.
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74-21-00
ALL ú ú C01 Page 1 ú Jul 15/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
TYPE 3 IGNITION LEAD AND SPARK IGNITER
Ignition Lead and Spark Igniter Figure 1 (Sheet 1)
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74-21-00
ALL ú ú C01 Page 2 ú Jul 15/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / /
CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
TYPE 4 IGNITION
TYPE 4 CONNECTOR
COOLING SHROUD
SPARK
IGNITER
COMBUSTION CASE BOSS
LEAD AND SPARK
IGNITER BRAIDED
CONDUIT
SEE B
COOLING AIR
WHITE CHAMFERED SILICONE SEAL
CONTACTS
CAPTIVE GASKET
IGNITER
BUSHING
SPARK IGNITER
GASKET
SEE C
TYPE 4 IGNITION LEAD AND SPARK IGNITER ON ENGINES PRE-SB 74-009
TYPE 4 CONNECTOR
COOLING SHROUD
SPARK
IGNITER
COMBUSTION CASE BOSS THREADED
CONNECTOR
B
INSULATOR
COOLING AIR
BLUE SYMMETRICAL SILICONE SEAL
CONTACTS
CAPTIVE GASKET
IGNITER
BUSHING
SPARK IGNITER
GASKET
SEE C
TYPE 4 IGNITION LEAD AND SPARK IGNITER
ON ENGINES POST-SB 74-009
F70653
Ignition Lead and Spark Igniter
Figure 1 (Sheet 2)
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