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ELECTROHYDRAULIC STEERING
bedplate. The bedplate is the top of an oil reservoir.
GEAR
Steering power is derived from either pumping
system acting alone. The system not in use serves as a
The steering gear is one of the most vital
standby source in case of an emergency.
auxiliaries aboard ship. It must be thoroughly
The two pumps (port and starboard) are identical
dependable and have sufficient capacity for maximum
in size and design and are of the variable delivery
maneuverability. The types of steering gear listed in
axial piston type. Each main pump unit includes a
the sequence of their development are (1) steam, (2)
built-in vane-type servo pump, pressure control and
electromechanical, and (3) electrohydraulic. Electro-
replenishing valves, and two main relief valves. Each
hydraulic steering gear was developed to meet the
main pump is stroked through a rotary servo control.
power requirements of naval vessels having large
displacements and high speeds with attendant increase
Each pump is driven by a 20-hp, 1200-rpm,
in rudder torques.
440-volt, 3-phase, 60-Hz induction motor through
reduction gears and a flexible coupling.
CONSTRUCTION
The pumps of the power unit are connected to the
The majority of steering gear installations in new
ram cylinders by a high-pressure piping system. The
construction naval vessels are of the electrohydraulic
two 4-way transfer valves are interposed in this
type. The electrohydraulic steering system installed in
piping, and their positions determine which pump is
one class of destroyer (fig. 11-15) consists essentially
connected to the cylinders in the ram unit. The hand
of (1) a ram unit, (2) a power unit, and (3) a remote
lever, which moves both valves simultaneously, is
control unit (not shown).
located on the power unit between the trick wheels. It
has three latched positions. The latched positions are
Ram Unit
marked P, N, and S, which denote port pump
connected, neutral (ram locked), and starboard pump
The ram unit is mounted athwartship and consists
connected, respectively.
of a single ram operated by opposed cylinders. The
ram is connected by links to the tillers of the twin
The transfer valves, which are of the ported piston
rudders. When oil pressure is applied to one end of the
type, are mounted on the power unit bedplate between
operating cylinder, the ram will move, causing each
the motors. When the valves are in the neutral (ram
rudder to move along with it. Oil from the opposite
locked) position, the ports of the pipes to the ram
end of the cylinder is returned to the suction side of
cylinders are blocked, and the two pipes from each
the main hydraulic pump in the power unit.
pump are connected through ported passages in their
respective valves. If either or both pumps are started
The tie rods that connect the two cylinders also
and put on stroke, oil will circulate through the valve
serve as guides for a sliding crosshead attached to the
and back to the pump. Movement of the transfer
ram to prevent the ram from rotating. The crosshead
valves in either direction connects the selected pump
also provides mechanical limits to the ram travel at 42
to the ram cylinders, and the opposite pump remains
of rudder angle. At this position the crosshead contacts
bypassed.
the copper facing on the stop collars and prevents
further movement.
The drain pipes from the ram cylinders lead to the
A rack is attached to the ram and engages two
reversible hand pump. It provides a means for
gears. The rotation of these gears is transmitted to the
emergency steering under limited rudder torques. The
respective differential control boxes through the
relief valve in the emergency steering system is set at
follow-up shaft.
500 psi. The oil flow is through pilot-operated
blocking valves that prevent the ram from over-
Power Unit
hauling the pump and kicking back the handles. When
you move the ram with the hand pump, set the main
The power unit has two independent pumping
transfer valves in the ram locked position and open
systems. These include two motor-driven pumps, two
the drain valves beneath the cylinders.
4-way transfer valves with operating gear, a relief
valve, two differential control boxes, two trick
The mechanical differential control box serves to
wheels, and a hand emergency gear all mounted on a
correlate the signal from the ram follow-up assembly

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