BUTTERFLY
SHAFT HEX
Bleed Air Regulator and PRSOV System Schematic
Figure 4
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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A 737-300/400/500MAINTENANCE MANUAL
The bleed air regulator contains a pneumatic pressure switch, reference pressure regulator, reverse flow switch assembly, relief valve assembly, and solenoid valve assembly mounted in or on a metal housing.
(1)
The pneumatic pressure switch is a pneumatically actuated electrical switch.
(2)
The reference pressure regulator is a bleed-on type regulator. The reference pressure regulator is composed of a spring loaded diaphragm, a poppet valve, and a combined valve guide and seat.
(3)
The reverse flow switch assembly is an electrical switch actuated by a spring loaded, differential pressure diaphragm acting through a lever assembly.
(4)
The relief valve assembly is a spring loaded closed, bleed-off type regulator containing a poppet valve, valve seat, and spring.
(5)
The solenoid valve assembly is a three-way ball valve actuated by a
dual coil, latching solenoid.Upstream pressure is ducted to the overpressure switch (shown in de-activated position), chamber D of the reverse flow switch assembly, and to the reference pressure regulator.The pressure passes through the normally open poppet valve of the reference pressure regulator to chamber A. Pressure is then ducted through the control orifice to the relief valve assembly and to the solenoid valve assembly.The solenoid valve assembly (shown in the open position) permits the control port, and PRSOV and 450°F thermostat connected to it, to be pressurized. Pressure is also vented to atmosphere through an orificed vent.As control port pressure rises, reference pressure regulator chamber A pressure rises. When chamber A pressure rises to a calibrated level, the force generated against diaphragm A overcomes spring force and moves the poppet valve toward the closed position.Closing the poppet valve decreases chamber A pressure and control port pressure. Decreased chamber A pressure permits spring force to open the poppet valve. This action modulates the poppet valve about a position which maintains the desired control port pressure.The solenoid valve assembly is a latching type valve, that is, when momentarily energized to a position, either open or closed, the valve is latched in that position until energized in the opposite direction.When the solenoid valve assembly is energized and latched in the closed position, the ball valve is moved upward to the opposite seat, closing off pressure from the reference pressure regulator and venting the control port to atmosphere.The pressure switch senses upstream pressure and is designed to operate an electrical switch when upstream port pressure rises above a calibrated level.The reverse flow switch assembly contains two pressurized chambers, chamber D and chamber E. The two chambers are separated by a diaphragm. A lever assembly, actuated by the diaphragm, operates an electrical switch.
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ALL ú ú 01 Page 10 ú Jul 15/96
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A
737-300/400/500MAINTENANCE MANUAL
L. Chamber E of the reverse flow switch assembly connects to the downstream pressure port. The diaphragm senses the differential pressure between upstream pressure port and downstream pressure port. When downstream pressure rises to a predetermined level above upstream pressure, the diaphragm operates the reverse flow switch through the lever assembly and switches an electrical signal to the closing coil of the solenoid valve assembly, shutting off control port pressure to the PRSOV.
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