(2)
AIRPLANES WITH FLOW CONTROL VALVES P/N 10-60704-7; At .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.
Equipment Mounting Shelves and Ducts
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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 E1-2, E2-1, E2-3, E3-1, E3-3 and E3-5 are hollow and have individual holes under the equipment for "draw through" cooling. There are sealing strips along the edges of these 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.
Airflow Detection System
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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 and an airflow detector (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.
B. The airflow detector consists of a temperature sensitive switch combined with a small heater. With airflow through the equipment cooling system, heat from the detector heater is dissipated. With loss of airflow the heat sensitive switch will close due to the heat rise. The airflow detector is installed in the blower inlet plenum.
C. The OFF amber warning light is located on the forward overhead panel (P5).
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
6. Check Valves
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A. Two check valves are installed in the equipment cooling system. These check valves are installed in the blower discharge duct for each blower and prevent cooling air being discharged back through the nonoperating blower.
7. Operation
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A. The operation of the equipment cooling system is automatic once electrical power is applied to the airplane. With the blower selector switch positioned to NORMAL the main blower will operate unless the BUS No. 1 is de-energized. If the main blower fails to operate, the blower selector switch may be positioned to ALTERNATE and the alternate blower will then operate.
(1)
AIRPLANES WITH FLOW CONTROL VALVES P/N 10-60704-1 THRU -6; The selected blower operates continuously and the flow control valve is in the open position when the differential pressure is less than
2.0 to 2.8 psi.
(2)
AIRPLANES WITH FLOW CONTROL VALVES P/N 10-60704-7; The selected blower operates continuously and the flow control valve is in the open position when the differential pressure is less than .7 to 1.1 psi.
B. When electrical power is connected to the airplane, circuit breaker panel P18-3 is energized and the blower and the airflow detector are energized. While the cabin pressure differential is low the blower creates the airflow necessary for cooling. In flight, cabin pressure differential increases causing a greater airflow through the blower duct. The increased airflow is sensed by the flow control valve which begins to close.
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