TM 5-5420-234-14&P
Section III. PRINCIPLES OF OPERATION
The function of the CBT is to allow a bridge company to rapidly transport bridge components that provide the means
for military load class 70 vehicular equipment or personnel to cross large, nonfordable streams or rivers.
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1.
Truck. Transports bridge components and support equipment to and from a bridge construction site. Also
provides basic electric power and hydraulic pressure that operates the LHS. Refer to TM 9-2320-279-10 for
specific technical principles of operation of the truck.
2.
LHS. The CBT is operated by using controls located in the cab or by using a hard-wired remote control unit
(RCU). The RCU can be operated from connectors located on the left or right side of the vehicle. BAP winch
operation is possible only from the RCU. Model A trucks include an analog type electrical system, while
Model B trucks are equipped with a digital type electrical system.
Electric power to operate the CBT is provided by a supply harness wired into the HEMTT electrical system.
The LHS MODE SELECT switch, RCU switches, and electrical relays located in the cab control box
determine which individual function is activated. Proximity switches mounted on the LHS permit simple load/
unload operation of the LHS when in the AUTO mode (cab controls only).
Hydraulic pressure is provided by a PTO-driven hydraulic pump located on the HEMTT transmission. The
CBT hydraulics are connected to the HEMTT chassis via quick-connect fittings.
Hydraulic pressure is controlled by relief valves and directional control valves. A vented relief valve limits
the maximum system pressure to 3100 psi (21,374 kPa). In addition, the winch circuit has tandem relief
valves that limit pressure in the winch circuit to 2100 psi (14,479 kPa).
Electrically activated directional control valves control the flow of fluid to individual components. When no
CBT functions are being used, a free-flow valve vents the main relief valve, which returns all fluid flow
directly to the reservoir. The moment a function is activated, the free-flow valve closes and pressurized oil is
delivered to the winch or LHS hydraulic cylinders.
Counterbalance (holding) valves located in the hydraulic cylinder manifolds support the payload whenever
hydraulic pressure is not provided. Transit valves in the main frame manifolds open during CBT transit
operations. This relieves the system of hydraulic pressure and allows the payload to be supported by the
physical structure rather than the system hydraulics.
3.
BAP. A special flatrack that contains a detachable winch frame assembly. When the BAP is loaded on the
CBT and secured to the LHS, it serves as the base support for interior or ramp bays during movement. It
provides a means to load and unload the interior ramp bays. It also converts the LHS into a ribbon bridge
launch and retrieval arm.
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