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DESCRIPTION
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The TC-4
modulating control valve is a cam operated,
graduating type control valve. The valve is used to control
the application and release of spring brake actuators, and is
generally mounted in the cab within easy reach of the driver.
Modulated control of the emergency brakes (spring brakes)
is effected by moving the valve's spring loaded lever. Moving
the lever against the resistance of the spring applies the
brakes and, allowing the valve handle to return, releases the
brakes.
When the valve is used for parking, the locking button is
moved into the locked position after the handle has been
moved to the "Brakes Applied" position. The lever is now
mechanically locked in position. To release the lever, the
lever is slightly depressed, the lock button moved out of the
locked position and the lever returned to the "Brakes
Released" position.
Porting consists of one (1) supply port, two (2) delivery and
two (2) exhaust ports.
OPERATION
Reference Figure 2, the TC-4
conjunction with a relay valve to control the application and
release of the spring brakes. In a typical system, the TC-4
valve and the relay valve receive supply air from the
emergency/parking reservoir.
RELEASED POSITION (Spring Brakes Released)
In the normal run position, air enters the supply port of the
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TC-4
valve, flows by the open inlet valve and out the delivery
port. Air flows to the service (control) port of the relay valve
causing the relay valve to deliver air to the spring brakes,
holding them in the released position.
APPLY POSITION (Spring Brakes Applied)
Moving the lever to the apply position allows the inlet valve
to close and the exhaust passage to open. This allows the
air being delivered to the service (control) port of the relay
valve to exhaust to atmosphere (through the exhaust of the
foot brake valve). With air exhausted from the service
(control) port of the relay valve, the relay valve responds,
exhausting the air from the spring brakes (allowing the brakes
to apply).
With sufficient air pressure in the emergency/parking
reservoir, modulation of the spring brake application is
possible; the amount of braking force governed by the
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position of the TC-4
valve lever.
With reference to Figure 2, note that the exhaust of the
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TC-4
valve is connected to a delivery line of the foot brake
valve. This prevents the compounding of spring brake and
service brake application forces on the slack adjusters.
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valve is generally used in
PREVENTIVE MAINTENANCE
Important: Review the Bendix Warranty Policy before
performing any intrusive maintenance procedures. A warranty
may be voided if intrusive maintenance is performed during
the warranty period.
No two vehicles operate under identical conditions, as a
result, maintenance intervals may vary. Experience is a
valuable guide in determining the best maintenance interval
for air brake system components. At a minimum, the TC-4
valve should be inspected every 6 months or 1500 operating
hours, whichever comes first, for proper operation. Should
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the TC-4
valve not meet the elements of the operational
tests noted in this document, further investigation and service
of the valve may be required.
Check for proper operation before placing vehicle in operation.
OPERATING AND LEAKAGE TESTS
If valve is to be tested on vehicle, block the vehicle wheels.
Build system pressure to approximately 100 psi and place
lever to "apply" position and observe that spring brakes
apply.
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With lever in apply position, lock lever in place with locking
button. Coat exhaust port with soap solution; leakage should
not exceed a 1" bubble in less than 5 seconds.
(NOTE: If line is connected to exhaust port, disconnect line
or remove pipe plug from other exhaust port.)
Excessive leakage would indicate a faulty inlet valve.
Release locking button and place lever in release position;
observe that brakes fully release. Coat exhaust port with
soap solution; leakage should not exceed a 1" bubble in not
less than 5 seconds. Excessive leakage would indicate
exhaust valve or lower o-ring leakage. (If line at exhaust port
was disconnected, connect line and/or tighten fitting or pipe
plug.)
Remove dial; while making a full foot valve application, coat
top of valve with soap solution. Leakage permitted is a 1"
bubble in not less than 5 seconds.
Excessive leakage would indicate upper o-ring leakage. (If
line is not connected to exhaust port, it will be necessary to
apply 100 psi to the exhaust port to check for upper o-ring
leakage.)
Soap area around supply port cap nut to check for cap nut
o-ring leakage. No leakage permitted.
Blow out or dry all soap solution and replace dial.
To check modulation of valve, it will be necessary to test
while vehicle is in motion. Select a suitable location to
perform braking test. With vehicle in motion, apply the TC-4
valve several times.
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