(2)
STBY AC and DC
(3)
MAN AC and DC
500
Oct 20/92 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-31-11 Page 803
EFFECTIVITY
AIRPLANES WITH OUTFLOW VALVE HEATED GASKET
OUTFLOW VALVE HEATED GASKET - MAINTENANCE PRACTICES
1. General
A. The gasket sealing the aft outflow valve to the airplane structure contains a heating element, thermostat and overheat fuse to provide heat in this area for cold high altitude flight to prevent the outflow valve freezing closed.
B. These procedures cover an adjustment test to assure operation of the heated gasket and removal/installation procedure should the heating element fail.
2. Heated Gasket Operation
A. The outflow valve heated gasket is powered by 115v ac from the P6 circuit breaker panel. Area temperature will be maintained between 40 ±5°F (4.4 ±2.7°C) and 70 ±5°F (21.1 ±2.7°C) by an integral thermostat. An integral fuse will open if the gasket temperature reaches approximately 160°F (71.1°C).
3. Heated Gasket Adjustment/Test
A. Equipment and Materials
(1) Means to cool gasket thermostat to approximately 35°F (1.7°C). Ice bag or ground air conditioning unit.
B. Prepare to test heated gasket
(1)
Pull six PRESSURIZATION CONTROL circuit breakers (P6).
WARNING: INADVERTENT OPERATION OF THE OUTFLOW VALVE MAY CAUSE SEVERE INJURY TO PERSONNEL.
(2)
Check OUTFLOW VALVE HEATER circuit breaker (P6) is open.
(3)
Provide electrical power (Ref 24-22-00 MP).
C. Test heated gasket.
(1)
Gain access to AFT OUTFLOW HEATER circuit breaker terminals located on P6-4 panel.
(2)
Check for resistance of 25-45 OHMS at breaker terminal 2.
(3)
If 25-45 OHM resistance exists at circuit breaker terminal 2 perform steps 5 and 6.
(4)
If the 25-45 OHM resistance does not exist at circuit breaker terminal 2, apply cold air or a heat sink (approx 32°F) to the outflow valve gasket thermostat until the resistance reading is obtained. Gasket thermostat location: within rectangular protrusion, where electrical lead wires originate on the outflow valve heater gasket.
(5)
Close AFT OUTFLOW HEATER circuit breaker and allow sufficient time (approx 10 minutes or less) for gasket thermostat to open.
(6)
Open AFT OUTFLOW HEATER circuit breaker and verify that resistance at circuit breaker terminal 2 indicates an open circuit.
(7)
CLOSE AFT OUTFLOW HEATER circuit breaker (P6).
4. Heated Gasket Removal/Installation A Remove cabin pressurization outflow valve (Ref 21-31-11 R/I).
B. Cut wires securing heated gasket to ship wiring and remove gasket.
C. Splice lead wires from new heated gasket to ship wiring. Maintain same wire length as original installation.
D. Install cabin pressurization outflow valve (Ref 21-31-11 R/I).
E. Perform heated gasket Adjustment/Test.
Feb 01/96 21-31-12 Page 201
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
Outflow Valve Heated Gasket 501
21-31-12Page 202 Figure 201 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Feb 20/85
PRESSURE CONTROLLER - REMOVAL/INSTALLATION
1. General
A. The pressure controller located on the top shelf of the forward equipment rack in the electronic equipment compartment is no problem to install. However, to properly engage the pressure controller electrically, an extractor-inserter tool is used. Refer to Chapter 20, Electrical/Electronic Black Box - Removal/Installation for proper use of the special tool.
B. After installation of new controller, check pressurization control system operation per 21-31-0, Pressurization Control System - Maintenance Practices.
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