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 8.  High Stage Regulator (Fig. 5)____________________
 A.  The high stage regulator is a device that functions to provide for regulation and shutoff of the high stage valve.
 B.  The high stage regulator includes a reference pressure regulator, reverse flow check mechanism, pneumatic shutoff, and a relief valve assembly.
 C.  The reference pressure regulator contains a diaphragm assembly and a poppet valve assembly consisting of a poppet valve, guide, spring and retainer. The reverse flow check mechanism is made up of two sections. A diaphragm section and poppet valve section are connected by an L shaped actuating lever. A seal on the lever isolates the two sections. The poppet valve section is vented to ambient and the poppet is normally spring loaded to the closed position. The rod arm of the poppet contacts one arm of the L shaped lever and the other arm of the lever is held in contact with the diaphragm by a spring. The diaphragm section of the reverse flow check mechanism consists of two chambers. One chamber contains a spring which forces the diaphragm into contact with the L shaped lever. The other chamber is connected to the downstream pressure connection and downstream test port.
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737-300/400/500MAINTENANCE MANUAL
 D.  The pneumatic shutoff is made up of a diaphragm, spring and ball valve with two seats. One seat is vented to ambient pressure. The opposite seat is open to upstream pressure. Chamber B side of the diaphragm is connected to the supply pressure connection and supply test port.
 E.  The relief valve assembly is a spring loaded poppet valve installed in a housing. Test ports are provided on the supply, control and downstream pressure connections to allow testing of the valve without disconnecting any lines.
 F.  Inlet air from the upstream source enters the supply pressure connection and is ported to the reference pressure regulator, reverse flow check mechanism and pneumatic shutoff. The air, ported to the reference pressure regulator, passes the metering poppet and is ported to Chamber A where it exerts pressure against the reference pressure regulator diaphragm. The diaphragm force overcomes the force of the reference pressure regulator spring and moves the metering poppet toward the closed position. When the forces are balanced, the pressure downstream of the reference pressure regulator is held at a constant value independent of the inlet pressure.
 G.  This constant reference pressure is then ported out the control pressure connection to the high stage valve.
 H.  The supply air source is ported to Chamber B of the pneumatic shutoff. When Chamber B pressure exceeds a prescribed limit, it overcomes the spring force acting on the diaphragm. This causes the poppet to stroke to the opposite seat from that shown, preventing inlet air from reaching the reference pressure regulator.
 I.  Downstream pressure from an external source is ported to the reverse flow check mechanism where it is compared to control pressure acting on the opposite side of the diaphragm. If downstream pressure rises to a predetermined level above the upstream pressure, the poppet is actuated open. This causes the reference pressure downstream of the control orifice to drop to a low level which closes the high stage valve.
 J.  A relief valve assembly provides pressure regulation in the event of a reference pressure regulator failure.
 9.  Pneumatic Ground Service Connection (Fig. 6)___________________________________
 A.  A pneumatic ground service connection is provided to allow pressurization of the pneumatic manifold by ground service carts. The connection is accessible through a hinged panel on the underside of the fuselage. The pressurized air supplied through this connection can be used for engine starts, the air conditioning system and other user systems. The connection also includes a check valve to prevent excessive pneumatic system leakage or reverse flow into the ground air source.
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 ALL  ú ú 01 Page 14 ú Jul 15/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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