(a)
The bleed shutoff valves and bleed air overheat switch (4900F) test covers the operation of the valves and relationship between the valve and the 4900F switch.
(b)
The bleed air isolation valve test covers only the operational testing of the valves.
(3)
The duct leakage test is intended to establish integrity and leakage limits of pneumatic ducts and associated components of the engine bleed air distribution system which are subject to pneumatic pressure.
(a) Time Pressure Drop Method
1) This leakage test, which requires no special equipment, measures the leakage on the right and left sides of the isolation valve. The leakage is measured by pressurizing the applicable side of the manifold with an APU and timing the pressure drop on the pneumatic supply indicator. a) The bleed air system test covers ducts from the APU shutoff valve to the
pack valve and through the engine bleed valve to the thirteenth stage modulating and shutoff valve, starter valve, precooler and eighth stage check valves. This test does not cover the ducts downstream of the pack valve.
(b) Flow Rate Method
1) These three leakage tests, which require special equipment, each check a separate section of the system. Each section of the system is isolated by closure of the appropriate valves and then pressurized using an air source equipped with a flow measuring indicator. a) The engine supply duct leakage test covers ducts between the modulating
and shutoff valve, starter valve, engine bleed valve and the eighth stage
check valves.
b) The pneumatic ducts downstream from engine bleed valves leakage test includes the ducts downstream of the engine bleed valves to the pack valve and APU bleed air valve. The test requires only the addition of one blocking plate and may be preferred if suspected leakage or questionable duct joints are located in these ducts. If ducts or components downstream of the pack valve are questionable, accomplish the pack installation pneumatic ducts leakage test.
c) The pack installation pneumatic ducts leakage test includes the ducts downstream of the engine and APU bleed valves and the ducts in the air conditioning equipment bay. Unless cargo compartment lining has been removed, it may be desirable to accomplish leakage test per (3)(b)1)b) before doing this test. If leakage per (3)(b)1)b) is within limits excessive leakage would be isolated to equipment bay ducts.
B. Bleed Air Shutoff Valves and Bleed Air Overheat Switch Test
(1)
Equipment and Materials
(a)
Controlled Heat Source - Temp. Cal probe heater (Attachment to Jet Cal engine analyzer), P/N BH3884-40, Howell Instruments Inc., 3479 W. Vickery Blvd., Ft. Worth, Texas 76107
(b)
TEMPCAL Tester, H394 Series, Howell Instruments Inc., 3479 W. Vickery Blvd., Ft. Worth, Texas 76107
(2)
Prepare to Test Bleed Air Distribution System
(a)
Open right engine cowl.
(b)
Connect external power and energize 115-volt ac transfer bus No. 1 and 2.
(c)
Check that the following circuit breakers are closed (P6).
1) MASTER CAUTION (ALL EXCEPT FUEL, if installed)
2) INDICATOR LTS, MASTER DIM BUS (9 places)
3) DIM & TEST (1 place)
4) BLEED AIR VALVE (2 places)
(3)
Test Bleed Air Shutoff Valves and Bleed Air Overheat Switch (490°F).
(a)
On forward overhead panel, press BLEED TRIP OFF light for operation.
(b)
On lightshield, press MASTER CAUTION light.
NOTE: Each annunciator and master caution light will go on when pressed, and off when released.
(c)
On forward overhead panel, position engine 1 BLEED switch to ON.
(d)
Check that bleed air valve from engine 1 opens as shown by valve external position indicator and that, after opening, valve motor stops.
CAUTION: VALVE MOTOR MUST STOP DRIVING AFTER VALVE IS OPEN. IF FAULTY LIMIT SWITCH ALLOWS MOTOR TO CONTINUE DRIVING (REBOUNDING) AFTER VALVE STOPS THE MOTOR MAY BE RUINED.
(e)
Remove bleed air overheat switch (490°F) from engine 1 pneumatic duct.
(f)
Apply 500°F controlled heat to switch probe.
CAUTION: DO NOT HEAT PROBE ABOVE 550°F. IF PROBE IS HEATED ABOVE 550°F, IT MAY BE DAMAGED.
(g)
Check that bleed air valve closes and after closing that valve motor stops; that BLEED TRIP OFF light on forward overhead panel, and MASTER CAUTION and AIR COND annunciation lights on lightshield panel illuminate.
CAUTION: VALVE MOTOR MUST STOP DRIVING AFTER VALVE CLOSES. IF FAULTY LIMIT SWITCH ALLOWS MOTOR TO CONTINUE DRIVING (REBOUNDING) AFTER VALVE STOPS THE MOTOR MAY BE RUINED.
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