Equipment Cooling System Component Location 563
21-58-0 Figure 1 Feb 15/77
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
2. Equipment Cooling Blowers
A. Two identical equipment cooling blowers are used in the equipment cooling system to create the required cabin-to-ambient differential pressure for inducing airflow through the system. Each blower is an axial flow type with an electrical motor mounted on the centerline of the blower cylindrical housing. Operation of the blower is continuous. The motor operates on 115-volt, three-phase power taken from circuit breaker panel P18-3 (Fig. 2) and is designed for continuous operation.
B. The blowers are in the lower aft section of the electronic compartment. They are connected between the blower inlet plenum and exhaust plenum by short flexible ducts and duct clamps and is secured by the blower support.
C. Equipment cooling blower operation is controlled by the blower selector switch on the overhead panel P5. The switch positions are NORMAL and ALTERNATE.
3. Automatic Flow Control Valve
A. The flow control valve is in the exhaust plenum under the floor in the aft section of the electronic compartment. The electronic compartment floor must be removed to gain access to the valve.
B. The automatic flow control valve is operated by airflow through the valve and sensed across its eccentrically mounted butterfly plate that acts as an airfoil. The butterfly valve, as an airfoil, provides initial movement toward the closed position at a given dynamic pressure. As the butterfly moves closed, an increased pressure differential is developed which acts on the off-centered butterfly to produce a closing torque.
(1)
AIRPLANES WITH FLOW CONTROL VALVES P/N 10-60704-1 THRU -6;
At 2.0 to 2.8 psi cabin-to-ambient differential pressure the flow control valve will be completely closed and the overboard flow is directed under the floor to the forward cargo compartment.
(2)
AIRPLANES WITH FLOW CONTROL VALVES P/N 10-60704-7; At 0.7 to 1.1 psi cabin-to-ambient differential pressure the flow control valve will be completely closed and the overboard flow is directed under the floor to the forward cargo compartment.
500
Feb 01/95 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-58-0 Page 3
T51719
Equipment Cooling System Circuit 514
21-58-0 Figure 2 Nov 15/76
Page 4
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
4. Equipment Mounting Shelves and Ducts
A. The electronic racks are formed by shelves, header plenums, and supporting structure. Holes for airflow are suitably located above each shelf. The holes lead to the header plenum, which leads into the ducts, and these into the blowers. The holes are sized to provide the right amount of cooling airflow when a given differential exists between cabin pressure and plenum pressure.
B. Shelves E3-1 and E3-3 are hollow and have individual holes under the equipment for "draw through" cooling. There are sealing strips along the edges of these two trays. The holes lead to the plenum, which leads into the ducts, and these into the blower.
(1) When changing orifice sizes because of component changes, total orifice inlet area for each shelf must be maintained at the same value. Refer to Equipment Cooling System -Balancing.
5. Airflow Detection System
A. The airflow detection system provides warning when the equipment cooling system is not supplying enough cooling air for safe electrical or electronic equipment operation. The airflow detection system consists of an equipment cooling OFF warning light, an aural warning horn and the system circuitry (Fig. 2). Electrical power for operation of the airflow detector and OFF light press-to-test circuit is taken from the 28-volt dc bus on circuit breaker panel P18. The OFF light is also connected to the master test circuit.
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