Spicer TPCS (Tire Pressure Control System) Service Manual - Manual (Page 8)

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Component Description
The following describes how each component of the
Tire Pressure Control System functions. Figure 1
shows the approximate location of each component.
Wheel Valve
All axles under tire pressure control incorporate a wheel
valve at each wheel end. Dual wheels are typically
connected to one wheel valve at the outer wheel to
provide tire pressure balance. When the system is idle,
the wheel valve isolates the tire(s) from the system,
thereby extending seal life since the seals are not under
constant pressure. The valve also ensures fail safe
operation should the system become disabled or
inoperable. The wheel valve provides for inflation of the
tires from the vehicle air supply via the pneumatic
controller, and deflation of the tires upon system
demand.
Electronic Control Unit (ECU)
The Electronic Control Unit is the control center for the
entire Tire Pressure Control System. The Electronic
Control Unit receives commands from the driver
through the Operator Control Panel and transmits
appropriate signals throughout the system. The
Electronic Control Unit is typically mounted in the cab
behind the passenger seat near the Pneumatic Control
Unit.
Operator Control Panel (OCP)
By using the Operator Control Panel keys, the operator
selects tire pressures for the conditions encountered.
The panel also displays such system parameters as
current tire pressures, selected modes, and system
status. The Operator Control Panel is typically mounted
on the dash within view and reach of the driver.
Pneumatic Control Unit (PCU)
The Pneumatic Control Unit is a solenoid controlled
manifold that receives commands from the Electronic
Control Unit and controls the air system. It also
contains the pressure transducer which transmits the
pressure readings to the Electronic Control Unit. The
Pneumatic Control Unit delivers the proper control
signal to the appropriate channel (steer/drive/trailer).
Speed Sensor
The speed sensor provides the Electronic Control Unit
with vehicle speed information. If the vehicle speed is
above programmed limits, the system will display an
overspeed indication on the Operator Control Panel.
Continued operation in this condition will cause the
system to automatically inflate the tires to a more
appropriate pressure.
Pressure Switch
The pressure switch acts as an electronic brake priority
switch. It prevents the Tire Pressure Control System
from consuming air from the wet tank until the brake
system is fully charged. This prevents the Tire Pres-
sure Control System from allowing the primary and
secondary tanks to go below recommended operating
pressures for braking.
Operation