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 (b)  In the event that the normal poppet fails to operate, the backup poppet will operate when differential pressure of
 9.70 |0.15 psi (66.9 |1 kPa) is sensed. After the poppet opens the sequence of valve operation is the same as with the normal poppet.
 NOTE: Valve test limits (Ref Adjustment/Test) differ from
____ operational limits above because valve is tested under no-flow conditions. Test specifications assure that valve meets operational pressure relief limits.
 (c)  When the overpressure condition is relieved, the control poppet closes and cabin air enters the servo chamber through the orifice. The servo piston moves under spring load to reseat the valve gate.

SYSTEMS CARD FILE
Overpressurization Indication Schematic Figure 2
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 PRESSURE RELIEF VALVE - REMOVAL/INSTALLATION
____________________________________________
 1.  General_______
 A.  There are three tasks in this procedure. The first task is the removal of the pressure relief valves. The second task is the installation of the pressure relief valves. The third task is a leak check of the positive pressure relief valves. The procedure has these parts:
 (1)  
The removal of power to the pressure relief valve

 (2)  
The removal of a sidewall lining to get access to the pressure relief valve

 (3)  
The removal of the pressure relief valve

 (4)  
The installation of the pressure relief valve

 (5)  
A functional test of the pressure relief valve

 B.  To get access to the pressure relief valves you must remove the sidewall lining from the left side of the forward cargo compartment.
 C.  The removal and installation procedure is the same for the upper or the lower pressure relief valve.
 TASK 21-32-01-004-001
 2.  Pressure Relief Valve Removal (Fig. 401)_____________________________
 A.  References
 (1)  
24-22-00/201, Manual Control

 (2)  
25-52-01/401, Containerized Cargo Compartment Ceiling and Sidewall Linings

 (3)  
AIPC 21-32-00, Fig. 1

 (4)  
WDM 21-33-11

 (5)  
SSM 21-33-01

 B.  Access
 (1)  Location Zone 123 Forward Cargo Container Compartment Aft Half, LH
 C.  Procedure
 S 864-002
 (1)  Open these circuit breakers and attach DO-NOT-CLOSE tags:
 (a)  P6 Main Power Distribution Panel
 1) 415K27 PACK TEMP CONT A
 2) 414C2 PACK TEMP CONT B
 3) 6F35 PACK TEMP CONT A
 4) 6F36 PACK TEMP CONT B

 S 014-003
 (2)  
Remove the sidewall lining from the left side of the forward cargo compartment at station 770 (Ref 25-52-01/401).

 S 034-004

 (3)  
Remove the electrical connector from the valve (upper valve - DS667, lower valve - DS668).

 (4)  
Remove the remote ambient sense line.

 S 034-005
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GATE 
SEE  A 
PRESSURE 
RELIEF 
VALVE 
(2 LOCATIONS)  INTEGRAL AMBIENT 
SENSE LINE 
ELECTRICAL  (2 LOCATIONS) 
CONNECTOR  SEE  B
(2 LOCATIONS) 
REMOTE AMBIENT 
SENSE LINE 

A  SEALANT (16 LOCATIONS) SCREW 
GASKET 
B 
Pressure Relief Valve Installation Figure 401 

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