SERVICE MANUAL
Fig. 3 Brake Valve Applied - Normal Operation
1 Plunger
9 Secondary Delivery
2 Spring Seat
10 Secondary Exhaust
3 Rubber Graduating
Valve Closed
Spring
11 Secondary Inlet
4 Primary Piston
Valve Open
5 Primary Exhaust
12 Secondary Supply
Valve Closed
13 Relay Cavity
6 Primary Delivery
14 Primary Supply
7 Two Bleed Passages
15 Primary Inlet
8 Relay Piston
Valve Open
Applying Normal Operation - Secondary Circuit
Portion of Brake Valve (Fig. 3)
When the primary inlet valve is moved off its seat, air is
permitted to pass through the bleed passage and enters
the relay cavity. The air pressure moves the relay piston
and the relay piston, which contains the exhaust seat,
closes the secondary exhaust valve. As the secondary
exhaust valve closes, the secondary inlet valve is moved
off its seat allowing secondary air pressure to flow put
the secondary delivery port. Because of the small
volume of air required to move the relay piston, action of
the secondary circuit portion of the valve is almost
simultaneous with the primary circuit.
Application - Loss of Air In Secondary Circuit (Fig. 4)
Should air be lost in the secondary circuit, the primary
circuit portion will continue to function as described under
"Normal Operation - Primary Circuit."
Fig. 4 Brake Valve Applied - Loss of Air In Secondary
Circuit
1
Primary Supply
2
No Air In Secondary Circuit
3
Primary Delivery
4
Secondary Delivery
Application - Loss of Air In Primary Circuit (Fig. 5)
Should air be lost in the primary circuit, the function will
be as follows. As the brake pedal is depressed and no
air pressure is present in the primary circuit supply and
delivery ports, the primary piston will mechanically move
the relay piston allowing the piston to close the
secondary exhaust valve and open the secondary inlet
valve and allow air pressure to flow out the secondary
delivery port.
Balanced - Primary Circuit of Brake Valve (Fig. 6)
When air pressure delivered to the brake actuators and
air pressure in the cavity of the delivery side of the
primary piston equals the mechanical force of the brake
pedal application, the primary piston will move and the
primary inlet valve will close, stopping the further flow of
air from the primary supply line through the valve. The
exhaust valve remains closed preventing any escape of
air through the exhaust port.
CTS-4079 CHAPTER IV
PRINTED IN UNITED STATES OF AMERICA
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