3
BALANCED: PRIMARY CIRCUIT PORTION
When the primary delivery pressure acting upon the primary
piston (2), equals the resultant mechanical force of the brake
treadle application, the primary piston will close preventing
further air flow from the supply to the delivery port of the
brake valve. The exhaust valve remains closed preventing
the escape of air through the exhaust port.
APPLYING: NORMAL OPERATION-
SECONDARY CIRCUIT PORTION
The relay piston moves down with the primary piston and
closes the secondary circuit exhaust. When the inlet valve
in the primary portion of the valve is moved off its seat, air
passes through the bleed passage in the lower portion of
the upper body and enters the relay piston cavity. The air
moves the relay piston (18) downward and opens the sec-
ondary inlet valve, allowing the air from the secondary supply
to flow out the delivery port of the same circuit.
APPLYING: LOSS OF AIR IN THE PRIMARY
CIRCUIT
If air is lost in the primary circuit, the valve will function as
follows: As the brake pedal is depressed and no air pres-
sure is present in the primary circuit, the primary piston (2)
will mechanically move the relay piston closing the second-
ary exhaust and opening the inlet valve of the same circuit
allowing air flow from the secondary supply to its associ-
ated delivery port.
APPLYING: LOSS OF AIR IN THE SECONDARY
CIRCUIT
If the air is lost in the secondary circuit, the primary circuit
will function as described above under Normal Operation:
Primary circuit portion.
FIGURE 7 - APPLYING - FAILURE IN THE SECONDARY
CIRCUIT
FIGURE 5 - APPLYING - NORMAL OPERATION
FIGURE 6 - APPLYING - FAILURE IN THE PRIMARY
CIRCUIT
PLUNGER
FORCE
7
2
8
DEL-1
DEL-2
SUP-1
SUP-2
EXHAUST
PLUNGER
FORCE
DEL-2
SUP-1
SUP-2
EXHAUST
2
DEL-1
PLUNGER
FORCE
7
2
8
DEL-1
DEL-2
EXHAUST
SUP-1
SUP-2
18
18
