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BALANCED: NO. 2 OR SECONDARY CIRCUIT
When the air pressure on the delivery side of the relay pis-
ton (20) approaches that being delivered on the primary side
of the relay piston, the relay piston moves closing the sec-
ondary 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 bal-
anced position in the primary circuit is reached as the air
pressure on the delivery side of the primary piston (22) equals
the effort exerted by the driver's foot on the treadle. A bal-
anced position in the secondary portion is reached when air
pressure on the secondary side of the relay piston (20) closely
approaches the air pressure on the primary side of the relay
piston.
When the brake treadle is fully depressed, both the primary
and secondary inlet valves remain open and full reservoir
pressure is delivered to the actuators.
RELEASING: NO. 1 OR PRIMARY CIRCUIT
With the brake treadle released, mechanical force is re-
moved from the spring seat (26), graduating spring (23), and
primary piston (22). Air pressure and spring load moves the
primary piston, opening the primary exhaust valve, allowing
air pressure in the primary delivery line to exhaust out the
exhaust port.
RELEASING: NO. 2 OR SECONDARY CIRCUIT
With the brake treadle released, air is exhausted from the
primary circuit side of the relay piston (20). Air pressure and
spring load move the relay piston, opening the secondary
exhaust valve, allowing air pressure in the secondary deliv-
ery line to exhaust out the exhaust port.
PREVENTIVE MAINTENANCE
Important: Review the warranty policy before performing
any intrusive maintenance procedures. An extended war-
ranty may be voided if intrusive maintenance is performed
during this period.
Because no two vehicles operate under identical conditions,
maintenance and maintenance intervals will vary. Experi-
ence is a valuable guide in determining the best maintenance
interval for any one particular operation.
Visually check for physical damage to the brake valve such
as broken air lines and broken or missing parts.
Every 3 months, or 25,000 miles or 900 operating hours:
Clean any accumulated dirt, gravel, or foreign material away
from the heel of the treadle, plunger boot, and mounting
plate.
OPERATION - Refer to Figure 3
APPLYING: NORMAL OPERATION - NO. 1 OR
PRIMARY CIRCUIT PORTION
When the brake treadle is depressed, the plunger exerts
force on the spring seat (26), graduating spring (23), and
primary piston (22). The primary piston, which contains the
exhaust valve seat, closes the primary exhaust valve. As
the exhaust valve closes, the primary inlet valve is moved off
its seat allowing primary air to flow out the No. 1 or primary
delivery port.
APPLYING: NORMAL OPERATION - NO. 2 OR
SECONDARY CIRCUIT
When the primary inlet valve (33) 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
(20), which contains the exhaust seat, and closes the sec-
ondary exhaust valve. As the secondary exhaust valve closes,
the inlet valve (13) is moved off its seat allowing the second-
ary air to flow out the delivery of the same circuit. Because
of the small volume of air required to move the relay piston
(20), action of the secondary circuit of the valve is almost
simultaneous with the primary circuit portion.
APPLYING: LOSS OF AIR IN THE NO. 2 OR
SECONDARY CIRCUIT
Should air be lost in the No. 2 or secondary circuit, the No.
1 or primary circuit will continue to function as described
above under
Normal Operation: No.1 or Primary Circuit Por-
tion
.
APPLYING: LOSS OF AIR IN THE NO. 1 OR
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 deliv-
ery ports, the primary piston (22) will mechanically move
the relay piston (20) , allowing the piston to close the sec-
ondary exhaust valve and open the secondary inlet valve
and allow air to flow out the secondary delivery port.
BALANCED: NO. 1 OR PRIMARY CIRCUIT
When the primary delivery pressure acting on the primary
piston (22) equals the mechanical force of the brake pedal
application, the primary piston (22) will move and the pri-
mary inlet valve (33) 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.
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