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 TM 55-1905-242-14
0006 00
Suction Filter
A suction filter, mounted at the bottom of the reservoir near the suction valve, provides initial filtration for the propulsion
engine hydraulic starting system.
Accumulator Gauges
Four accumulator gauges, one for each accumulator, monitor hydraulic pressure within the accumulators. The gauges are
connected to the accumulator piping by flexible hoses and may be isolated from the system by closing the gauge valves. A
gauge mounted in the pilothouse console near the rudder angle indicator allows the operator to monitor starting system
pressure. When the isolation valve, located near the hand pump, is closed, the pilothouse gauge reads the pressure present
in the port side of the system. When the isolation valve is open, the pressure equalizes across both sides of the system, and
the pilothouse gauge reads this pressure.
HYDRAULIC STEERING SYSTEM
General
The LCM-8 Mod 2 uses a hydraulic steering system to actuate the rudders, which in turn steer the vessel. The system
consists of two engine-driven hydraulic pumps, a flow divider, a helm unit, two steering cylinders, a relief valve, three check
valves, two counterbalance valves, two isolation valves, two bypass valves, two suction valves, two suction strainers, a
drain valve, a return filter, a reservoir, and a pilothouse gauge.
Engine-Driven Hydraulic Pump
Two engine-driven hydraulic pumps provide the hydraulic power necessary to operate the hydraulic steering system. Each
propulsion engine has a separate pump allowing full operation of the hydraulic steering system even with only one propul-
sion engine running. Each engine-driven hydraulic pump has a flow rate of 1.5 gal/min (5.7 L/min).
Flow Divider
All discharge flow from the engine-driven hydraulic pumps is routed through a flow divider which is set at 1050 lb/in2 (72.4
bar). The flow divider supplies 2 gal/min (7.6 L/min) of hydraulic oil to the helm unit throughout a wide range of pump speeds.
This constant oil flow rate permits consistent helm operation at all engine speeds. All excess flow reaching the flow divider
is returned to the reservoir through the return filter.
Helm Unit
The helm unit receives hydraulic oil from the engine-driven hydraulic pumps and directs the oil as needed to position the
rudders. When the wheel is stationary, all the hydraulic oil supplied to the helm unit is returned to the reservoir through the
return filter, and the rudders remain stationary. When the wheel is turned, the oil is discharged from the helm unit through the
counterbalance valves and isolation valve to the hydraulic cylinders, which turn the rudders. Direction of hydraulic oil flow
is determined by the direction of wheel rotation. In the event of failure of both engine-driven hydraulic pumps, the helm unit
is capable of acting as a pump to allow continued operation of the steering system.
Steering Cylinder
Two steering cylinders are used to turn the rudders. The cylinders are mounted outboard and aft of the rudder stocks, port
and starboard. The rudders and steering cylinders are synchronized by a tie rod connecting the two rudder arms.
Relief Valve
A relief valve, mounted in the line between the engine-driven hydraulic pump and the helm unit, prevents system damage
caused by overpressurization. The relief valve is set at 1000 lb/in (68.9 bar). Once the system pressure exceeds the relief
valve setting, all excess pressure is returned to the hydraulic reservoir through the return filter.
0006 00-4
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