2
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 to flow out the secondary delivery port.
BALANCED: PRIMARY CIRCUIT
When the primary delivery pressure acting on the piston
equals the mechanical force of the brake pedal application,
the primary piston will move and the primary inlet valve will
close, stopping 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.
BALANCED: SECONDARY CIRCUIT
When the air pressure on the secondary side of the relay
piston approaches that being delivered on the primary side
of the relay piston, the relay piston moves closing the
secondary inlet valve and stopping further flow of air from the
supply line through the valve. The exhaust remains closed
as the secondary delivery pressure balances the primary
delivery pressure.
When applications in the graduating range are made, a
balanced position in the primary circuit is reached as the air
FIGURE 3 - E-6
™
DUAL BRAKE VALVE SECTIONAL
DIAGRAM
14
30
32
31
33
28
15
9
11
10
25
16
12
13
20
21
24
23
22
27
26
17
19
18
7
8
18
4
5
19
1
2
6
16
17
APPLYING: NORMAL OPERATION -
SECONDARY CIRCUIT
When the primary inlet valve is moved off its seat, air is
permitted to pass through the bleed passage and enters the
relay piston cavity. The air pressure moves the relay piston,
which contains the exhaust seat and closes the secondary
exhaust valve. As the secondary exhaust valve closes, the
secondary inlet valve is moved off its seat allowing the
secondary air to flow out the secondary delivery port.
Because of the small volume of air required to move the
relay piston, action of the secondary circuit of the valve is
almost simultaneous with the primary circuit portion.
APPLYING: LOSS OF AIR IN THE SECONDARY
CIRCUIT
Should air be lost in the secondary circuit, the primary
circuit will continue to function as described above under
Normal Operation: Primary Circuit Portion.
APPLYING: LOSS OF AIR IN THE PRIMARY
CIRCUIT
Should air be lost in the primary circuit, the function will be
as follows: As the brake treadle is depressed and no air
pressure is present in the primary circuit supply and
FIGURE 4 - E-10
™
DUAL BRAKE VALVE SECTIONAL
DIAGRAM
34
