(2)
The valve uses two control metering sections. The primary metering section uses a remote ambient sense line and limits the differential pressure to 8.95 psi. The secondary metering section (backup control) uses an integral ambient sense tube. This section limits the differential pressure to 9.42 psi.
(3)
At a cabin-to-ambient differential pressure of 8.95 psi or higher, the head pressure is vented overboard allowing cabin pressure to force the poppet open. This vents cabin air overboard. An indicator flag on each of the valve flappers holds the flappers from going completely closed. The outside edges of the flappers are painted red and give visual indication that the valve has opened. Pulling the flappers open from outside the airplane and tucking the flag back into the valve resets visual indication of valve operation.
B.
Vacuum Relief Valve (Fig. 2)
___________________
(1) Two vacuum relief valves, located in the forward fuselage skin, provide negative pressure relief. The valves are spring-loaded closed flapper type doors. Negative pressure of -0.3 psi on the valve opens the door inward allowing air into the cargo compartment.
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A
757
MAINTENANCE MANUAL
CSEE POSITIVE VALVES RELIEF PRESSURE
SEE B
SEE A
BASE
FWD A REMOTE AMBIENT SENSING TUBE A COVER SECTION METERING SECONDARY
FWD INBD SECTION METERING PRIMARY A
FILTER
B C
LINE SENSE AMBIENT STATIC SECONDARY INTEGRAL SECTION METERING FILTER STATIC REMOTE LINE BALL AMBIENT SENSE SECTION METERING PRIMARY FLAPPER FLAG INDICATOR RED PAINTED INDICATOR FLAG
BALANCE DIAPHRAGM POPPET D
FLAPPER A-A D INDICATOR FLAG SEE
Figure 1 Positive Pressure Relief Valve
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A
757
MAINTENANCE MANUAL
Vacuum Pressure Relief Valve
Figure 2
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A
757 MAINTENANCE MANUAL
POSITIVE PRESSURE RELIEF VALVE - MAINTENANCE PRACTICES
______________________________________________________
1. General_______
A. This procedure has instructions to do the tasks that follow:
(1)
Remove the Positive Pressure Relief Valves
(2)
Install the Positive Pressure Relief Valve
(3)
Replace the Relief Valve Filter
(4)
Positive Pressure Relief Valve Test with Boeing Test Equip A21010-57
TASK 21-32-01-002-001
2. Remove the Positive Pressure Relief Valve (Fig. 201)_________________________________________
A. References
(1)
AMM 06-46-00/201, Entry, Service and Cargo Doors, Access Doors and Panels
(2)
AMM 25-50-02/401, Sidewall Lining
B.
Access
(1)
Location Zone
153 Aft cargo compartment (Left)
C.
Prepare for the Removal
S 012-002
(1)
Open the aft cargo door, 822 (AMM 06-46-00/201).
S 012-003
(2)
Remove the left sidewall lining (STA 1400-1410) that is 20 feet aft of the forward bulkhead of the aft cargo compartment (AMM 25-50-02/401).
S 012-004
(3)
Remove the duct(s) that are neccessary to get access to the relief valves.
D.
Remove the relief valve.
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