G. Honest Orifice Cleaning
SUBTASK 30-21-11-020-006
(1) Do the following to remove the honest orifice [4]:
(a) Remove the lockwire [1].
(b) Remove the screw [2] and washer [3].
(c) Remove the honest orifice [4].
SUBTASK 30-21-11-170-001
(2) Clean the orifice with one of the following methods:
(a) Method one uses compressed air.
1) Apply an air source, STD-6638, through the orifice from the threaded end and at
each of the four vent holes.
2) If necessary, use a 0.032 in. (0.813 mm) lockwire to clean out the internal hole of
the honest orifice.
(b) Method two uses ultrasonic cleaning:
1) Put the orifice in a solution of Turco C MXP, B50270, for 4 to 6 minutes.
2) Flush the orifice internally and externally with clean water at high pressure.
3) Put the removable orifice in a beaker with the open end of the orifice down and fill
the beaker with the Turco C MXP, B50270.
4) Put the beaker in an ultrasonic cleaner, STD-182, and fill the tank with water until
the water level is 0.375 in. (9.525 mm) from the top of the beaker.
5) Operate the ultrasonic cleaner for 5 minutes.
6) Remove the orifice from the beaker and discard the dirty cleaning solution.
7) Flush the orifice and beaker with the cleaning solution using a squeeze bottle,
STD-6462.
8) Put the removable orifice back in the beaker with the open end of the orifice down
and fill the beaker with the cleaning solution.
9) Operate the ultrasonic cleaner for another 5 minutes.
10) Repeat the process from step 6 until the cleaning solution is clear after a 5 minute
period of operation in the ultrasonic cleaner.
SUBTASK 30-21-11-100-001
(3) Use a swab, G01659 to carefully clean and wipe up dirt from the following:
NOTE: Be careful not to allow dirt to drop down into the hole.
(a) Valve Housing.
(b) Honest Orifice threads.
SUBTASK 30-21-11-420-003
CAUTION
OBEY THESE INSTRUCTIONS. IF YOU INSTALL THE HONEST ORIFICE
INCORRECTLY, HOT AIR LEAKS WILL CAUSE DAMAGE TO EQUIPMENT.
(4) Use thread lubricating compound for the assembly of all threaded parts as follows:
737-600/700/800/900
AIRCRAFT MAINTENANCE MANUAL
30-21-11
Page 702
D633A101-ILF Feb 15/2019
ECCN 9E991 BOEING PROPRIETARY - Copyright © Unpublished Work - See title page for details
EFFECTIVITY
ILF ALL; AIRPLANES WITH ENGINE COWL TAI
VALVE P/N 3215618-5
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