Removal of the Recirculation Check Valve

TASK 21-21-42-000-001-A
Removal of the Recirculation Check Valve

WARNING: MAKE SURE THAT AIR IS NOT SUPPLIED TO THE AIR CONDITIONING SYSTEM FROM THE MAIN ENGINE, THE APU OR A GROUND SOURCE. HOT COMPRESSED AIR CAN CAUSE INJURY TO PERSONNEL.

NOTE: The procedure is the same for the recirculation check valves 4020HM (4021HM).

FIN: 4020HM
FIN: 4021HM

1. Reason for the Job
Self explanatory
2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment

REFERENCE	QTY	DESIGNATION
No specific	1	ACCESS PLATFORM 2M (6 FT)
No specific	AR	PLUG - BLANKING
No specific	AR	SAFETY CLIP - CIRCUIT BREAKER
No specific	AR	WARNING NOTICE(S)

B. Work Zones and Access Panels

ZONE/ACCESS	ZONE DESCRIPTION
825

C. Referenced Information

REFERENCE	DESIGNATION
TASK 24-41-00-861-002-A	Energize the Aircraft Electrical Circuits from the External Power
TASK 24-41-00-861-002-A-01	Energize the Aircraft Electrical Circuits from the APU
TASK 24-41-00-861-002-A-02	Energize the Aircraft Electrical Circuits from Engine 1(2)
TASK 25-54-12-000-001-A	Removal of the Forward Cargo-Compartment Partition
TASK 52-30-00-860-001-A	Open the FWD or Aft Cargo-Compartment Door with the Yellow Electric Pump
Recirculation Check Valve 4020HM (4021HM).
FOR [4020HM] (RECIRC CHECK VALVE 1)
TASK 06-41-53-00	FUSELAGE-DESCRIPTION AND OPERATION
FOR [4021HM] (RECIRC CHECK VALVE 2)
TASK 06-41-53-00	FUSELAGE-DESCRIPTION AND OPERATION

3. Job Set-up
Subtask 21-21-42-861-050-A

A. Energize the aircraft electrical circuits (Ref. AMM TASK 24-41-00-861-002).

Subtask 21-21-42-865-050-A

B. Open, safety and tag this(these) circuit breaker(s):

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C ALL
FOR FIN: 4020HM (RECIRC CHECK VALVE 1)
122VU	AIR COND/RECIRC FAN/L/CTL	2HG	X20
122VU	AIR COND/RECIRC FAN/L/SPLY	1HG	X18
FOR FIN: 4021HM (RECIRC CHECK VALVE 2)
122VU	AIR COND/RECIRC FAN/R/CTL	11HG	W20
122VU	AIR COND/RECIRC FAN/R/SPLY	3HG	W18

Subtask 21-21-42-941-050-A

C. Safety Precautions
(1) On AIR COND panel 30VU:
(a) Make sure that:
1 The APU BLEED pushbutton switch is in the off position (the ON legend is off).
2 The ENG 1 BLEED and the ENG 2 BLEED pushbutton switches are in the off position (the OFF legends are on).
(b) Put a WARNING NOTICE(S) in position to tell the persons not to operate these pushbutton switches.
(2) On the High Pressure (HP) ground connector put the WARNING NOTICE(S) in position to tell persons not to supply ground air.

Subtask 21-21-42-010-050-A

D. Get Access
(1) Open FWD cargo-compartment door 825 (Ref. AMM TASK 52-30-00-860-001).
(2) Put an ACCESS PLATFORM 2M (6 FT) in position at FWD cargo-compartment door 825.
(3) Remove the access panel(s) from partition FR34 (Ref. AMM TASK 25-54-12-000-001):
(a) FOR [4020HM] (RECIRC CHECK VALVE 1)

(Ref. AMM D/O 06-41-53-00),

(b) FOR [4021HM] (RECIRC CHECK VALVE 2)

(Ref. AMM D/O 06-41-53-00).

4. Procedure
Subtask 21-21-42-020-050-A

A. Removal of the Recirculation Check Valve
(1) Remove the clamp (4) and disconnect the sleeve (5).
(2) Remove the clamp (1).
(3) Carefully remove the flange (3) together with the recirculation check valve (2).
(4) Remove the recirculation check valve (2) from the flange (3).
(5) Put the PLUG-BLANKING in each disconnected line end.

[Rev.10 from 2021] 2026.04.02 06:10:54 UTC