Bendix Commercial Vehicle Systems TC-7 TRAILER CONTROL BRAKE VALVE - Manual (Page 2)

2
Because of its use as a trailer service brake control valve,
the TC-7
™ valve should NOT be used in lieu of the vehicle
parking brakes. The handle is marked NOT FOR PARKING.
In general the TC-7
™ valve should not be in use and left
unattended.
OPERATION
APPLYING
When the handle or actuating lever is moved in a clockwise
direction from the released position, force is exerted on the
pressure graduating spring through the action of the cam
and cam follower. The force of the spring on the piston causes
it to move down.
The exhaust seat, which is in the center of the piston,
contacts the exhaust valve and closes the exhaust passage
in the piston. The continued downward movement of the
piston moves the inlet valve-off its seat. Reservoir air
pressure flows by the open inlet valve and out the delivery
port.
HOLDING
The air pressure that flows by the open inlet valve also
becomes effective on the bottom area of the piston. As the
force of the air pressure beneath the piston balances the
force of the depressed graduating spring above, the piston
lifts slightly and the inlet valve returns to its seat. The exhaust
valve remains seated so the flow of air through the valve is
stopped and air pressure in the service line is held.
RELEASING
When the handle or operating lever is moved in a
counterclockwise direction the force above the piston is
decreased. The air pressure beneath will then lift the piston,
moving it away from the exhaust valve. With the exhaust
passage open, air pressure in the service line will exhaust
out the exhaust port of the valve.
PREVENTIVE MAINTENANCE
Important: Review the warranty policy before performing
any intrusive maintenance procedures. An extended warranty
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. Experience
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, 25,000 miles (40,000 km.) or 900 operating
hours perform Operating and Leakage Tests.
SERVICE CHECKS
OPERATING TEST
Park the vehicle on a level surface and block the wheels.
Connect an accurate test gauge to the delivery port of the
TC-7
™ valve or connect the gauge to the service hose
coupling of the tractor. When the gauge is connected to the
service hose coupling, install a dummy hose coupling on
the supply (emergency) hose coupling and place the tractor
protection control in the trailer charging position. When the
TC-7
™ valve handle is moved to the fully applied position,
the gauge should register full reservoir pressure.
NOTE: Some valves may be preset to deliver lower than
reservoir pressure; however, the standard valves
generally used on tractors are set to deliver full
reservoir pressure. Intermediate positions should
deliver proportional intermediate pressures. Upon
release, the gauge should immediately register zero.
LEAKAGE TEST
Locate the exhaust port or exhaust line and apply a soap
solution. (It is common practice to connect a line from the
valve exhaust port to a location remote from the immediate
driver’s area.) With the valve in the released position, exhaust
leakage should not exceed a 1" bubble in 5 seconds (100
sccm).
With the valve fully applied, leakage at the exhaust should
not exceed a 1" bubble in 3 seconds (175 sccm).
If the valve does not function as described or leakage is
excessive, it is recommended that it be replaced with a new
or remanufactured unit, or repaired with genuine parts
available at Bendix outlets.
REMOVAL & INSTALLATION
The removal, disassembly, assembly and installation
procedures are number keyed to the sectional and exterior
views of the TC-7
™ valve in Figure 1.
REMOVAL
1. Block the wheels or hold the vehicle on a level surface
by means other than air brakes.
2. Drain all air pressure from all reservoirs.
3. Identify the air lines and connections and remove from
the TC-7 ™ valve.
4. Consult the vehicle manual for instructions on
disassembly of the steering column components.
NOTE: Some TC-7 ™ valve installations will be on the exterior
of the steering column, in which case Step 4 can
be disregarded.