Pressurization Relief Valves Location 500
21-32-0Page 2 Figure 1 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Nov 15/67
2. Safety Relief Valves (Fig. 2)
A. Two safety relief valves acting independently of each other and all other systems prevent the cabin-to-ambient pressure differential from exceeding 8.5 psi.
B. Each valve consists of a poppet valve, control chamber, and a spring-loaded diaphragm operated sensor control for controlling the valve opening. The control chamber is vented to the cabin, but has a restrictor in the vent for limiting cabin air inflow. A filter is also installed to prevent contamination in the control chamber. Another passage vents to ambient through the diaphragm operated sensor control poppet.
C. The sensor control is separated by a diaphragm. One side of the diaphragm senses cabin pressure while the other side senses ambient pressure. A differential pressure of 8.5 psi will cause the poppet to unseat opening a vent from the control chamber to ambient. This venting of the control chamber reduces the pressure within the chamber.
D. The valve gate, with control chamber pressure on one side will cause the gate to unseat at approximately 8.5-psi differential pressure as a result of cabin pressure on the other side of the valve gate. The diaphragm operated sensor control ensures that cabin-to-ambient differential pressure does not exceed 8.50 psi.
E. The safety relief valves are installed under the fuselage approximately opposite the aft entry door. One safety relief valve is installed on each side of the outflow valve.
3. Pressure and Relief Valve
A. The pressure and relief valve prevents a negative pressure differential from becoming great enough to damage the airplane during emergency descent with no airplane air input from the air conditioning system. The valve consists of a spring-loaded door which relieves automatically. The valve is located forward and above the upper safety relief valve (Fig. 1).
500
Jun 20/92 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-32-0 Page 3
Safety Relief Valve Schematic 500
21-32-0 Figure 2 Nov 15/68
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
4. Pressure Equalization Valves
A. An equalization valve is provided at the aft bulkhead of each cargo compartment. (See figure 1.) These valves keep the pressure in the cargo compartments and the cavities surrounding them at approximately the same pressure should the cabin pressure vary.
B. Each equalization valve contains two valve flappers. One flapper hinges away from the cargo compartment and the other hinges toward the cargo compartment. Each valve is accessible from within the cargo compartment where it is installed.
5. Blowout Panels
A. Three blowout panels are located in the forward cargo compartment and one is located in the aft cargo compartment. These panels are designed to maintain isolation of the cargo compartments during normal service but will blow out to protect structure at a differential pressure of approximately 1 psi.
B. In the forward cargo compartment one blowout panel is located in the forward bulkhead, another is in the aft bulkhead, and the third is located in the ceiling lining. The blowout panel in the aft cargo compartment is located in the ceiling lining. (See figure 1.)
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Nov 15/66 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-32-0 Page 5
PRESSURE AND RELIEF VALVE - REMOVAL/INSTALLATION
1. General
A. The pressure and relief valve is a spring-loaded flapper valve which opens when ambient pressure exceeds cabin pressure.
2. Equipment and Materials
A. Spring scale - push type
B. Deleted
3. Remove Valve (Fig. 401)
A. Remove right panel from aft cargo compartment aft bulkhead.
B. Remove valve hinge bolts.
C. Disengage spring from frame anchor hole and remove valve door from frame.
NOTE: Spring should not be allowed to snap out of frame anchor hole. Restrain spring and lower to rest against valve door.
D. Remove fasteners holding spring support retainer and remove retainer.
E. Hold spring securely, remove spring support rod, disengage spring from valve door anchor hole, and allow spring to unwind.
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