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 TM 55-1925-273-10-1
OPERATOR'S MANUAL
INLAND AND COASTAL LARGE TUG (LT)
THEORY OF OPERATION
HYDRAULIC SYSTEMS
GENERAL
The LT is provided with three separate hydraulic systems. These systems are: the steering gear hydraulic system, the central
hydraulic system, and the towing machine hydraulic system. Each system has its own pumps, filters, piping, reservoir, and
controls.
THE STEERING GEAR HYDRAULIC SYSTEM
The steering gear hydraulic system is an electrically driven system (figures 1 and 2). The main function of the steering gear
hydraulic system is to power the rudder actuators in response to steering commands from the helm or auxiliary stations.
The system components of the steering gear hydraulic system consist of: the helm station, an oil reservoir, two unit pumps,
a surge arrestor, an emergency hand pump, rudder actuators, solenoid actuated hydraulic valves (maneuvering valves), and
three auxiliary steering stations. The emergency hand pump (figure 2) provides hydraulic pressure and directional control to
the steering gear when electrical control has been lost at the helm or auxiliary stations. Refer to WP 0024 00 for further
details.
THE CENTRAL HYDRAULIC SYSTEM
The central hydraulic system (figures 3, 4, 5) provides hydraulic power for the crane, the capstan, tow pins, and anchor
windlass. It may also be aligned to provide hydraulic power to both towing machines. A crossover allows the towing ma-
chine hydraulic system (figure 6) to power the central hydraulic system (figure 3) in the event of failure of the central
hydraulic system (figure 4) or power pack (figure 6). The central hydraulic system (figure 3, 4, and 5) is comprised of a
hydraulic fluid reservoir, two pump units, filter, and control panel. Refer to WP 0039 00 for further details.
TOWING MACHINE HYDRAULIC SYSTEM
The towing machine hydraulic system (figure 6) provides hydraulic power for the port and starboard towing machines. It
may also be aligned to provide hydraulic power the central hydraulic system (figures 3, 4, and 5). The hydraulic towing
machine system consists of: a diesel engine (pump drive engine), a pump unit, a reservoir, and a hydraulic oil cooler.
PUMP DRIVE ENGINE
The pump drive engine, located in AMS 1 (starboard side), powers a dual pump, open-loop hydraulic system. The maximum
hydraulic flow is proportional to the pump drive engine's speed. The hydraulic fluid flow is controlled by a proportional
directional control valve (figure 6, item 1) mounted on the towing machine drive motor. The pilot signal to the directional
control valve is from the remote control lever located on the operator's console. A crossover allows this hydraulic system
(figure 6) to power the central hydraulic system (figures 3, 4, and 5) in the event of failure of the central hydraulic system
(figure 4).
OIL RESERVOIR
The oil reservoir stores the hydraulic fluid for the hydraulic towing machine system.
HYDRAULIC OIL COOLER
The hydraulic oil cooler (figure 6, item 2) (located at the reservoir) uses raw water to cool hydraulic fluid that was heated
while operating the towing machine.
0025 00-1
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