SERVICE MANUALFig. 3 Brake Valve Applied - Normal Operation1 Plunger9 Secondary Delivery2 Spring Seat10 Secondary Exhaust3 Rubber GraduatingValve ClosedSpring11 Secondary Inlet4 Primary PistonValve Open5 Primary Exhaust12 Secondary SupplyValve Closed13 Relay Cavity6 Primary Delivery14 Primary Supply7 Two Bleed Passages15 Primary Inlet8 Relay PistonValve OpenApplying Normal Operation - Secondary CircuitPortion of Brake Valve (Fig. 3)When the primary inlet valve is moved off its seat, air ispermitted to pass through the bleed passage and entersthe relay cavity. The air pressure moves the relay pistonand the relay piston, which contains the exhaust seat,closes the secondary exhaust valve. As the secondaryexhaust valve closes, the secondary inlet valve is movedoff its seat allowing secondary air pressure to flow putthe secondary delivery port. Because of the smallvolume of air required to move the relay piston, action ofthe secondary circuit portion of the valve is almostsimultaneous with the primary circuit.Application - Loss of Air In Secondary Circuit (Fig. 4)Should air be lost in the secondary circuit, the primarycircuit portion will continue to function as described under"Normal Operation - Primary Circuit."Fig. 4 Brake Valve Applied - Loss of Air In SecondaryCircuit1Primary Supply2No Air In Secondary Circuit3Primary Delivery4Secondary DeliveryApplication - Loss of Air In Primary Circuit (Fig. 5)Should air be lost in the primary circuit, the function willbe as follows. As the brake pedal is depressed and noair pressure is present in the primary circuit supply anddelivery ports, the primary piston will mechanically movethe relay piston allowing the piston to close thesecondary exhaust valve and open the secondary inletvalve and allow air pressure to flow out the secondarydelivery port.Balanced - Primary Circuit of Brake Valve (Fig. 6)When air pressure delivered to the brake actuators andair pressure in the cavity of the delivery side of theprimary piston equals the mechanical force of the brakepedal application, the primary piston will move and theprimary inlet valve will close, stopping the further flow ofair from the primary supply line through the valve. Theexhaust valve remains closed preventing any escape ofair through the exhaust port.CTS-4079 CHAPTER IVPRINTED IN UNITED STATES OF AMERICAPage 4
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