Figure 10-11.-Electrohydraulic steering mechanism.
in figure 10-11 will help you to understand the general
Getting Planes on Deck
principles of their operation. As the hand steering wheel
turns in a counterclockwise direction, its motion turns
the pinion gear (g). This causes the left-hand rack (rl) to
move downward and the right-hand rack (rz) to move
upward. Notice that each rack attaches to a piston (pl or
p2). The downward motion of rack r] moves piston p]
downward in its cylinder and pushes the oil out of that
cylinder through the line. At the same time, piston pz
moves upward and pulls oil from the right-hand line into
the right-hand cylinder.
If you follow these two lines, you see that they enter
a hydraulic cylinder (S). One line enters above and one
below the single piston in that cylinder. This piston and
the attached plunger are pushed down toward the
hydraulic pump (h) in the direction of the oil flow shown
in the diagram. So far in this operation, hand power
has been used to develop enough oil pressure to move
the control plunger attached to the hydraulic pump. At
this point, an electric motor takes over and drives the
pump (h).
Oil is pumped under pressure to the two big steering
rams (RI and R?). You can see that the pistons in these
rams connect directly to the rudder crosshead that
controls the position of the rudder. With the pump
operating in the direction shown, the ship’s rudder is
thrown to the left, and the bow will swing to port. This
operation shows how a small force applied on the
steering wheel sets in motion a series of operations that
result in a force of thousands of pounds.
The swift, smooth power required to get airplanes
from the hanger deck to the flight deck of a carrier is
provided by a hydraulic lift. Figure 10-12 shows how
this lifting is done. An electric motor drives a
variable-speed gear pump. Oil enters the pump from the
reservoir and is forced through the lines to four
hydraulic rams. The pistons of the rams raise the
elevator platform. The oil under pressure exerts its force
on each square inch of surface area of the four pistons.
Since the pistons are large, a large total lifting force
results. Either reversing the pump or opening valve 1
and closing valve 2 lowers the elevator. The weight of
the elevator then forces the oil out of the cylinders and
back into the reservoir.
Operating Submarines
Another application of hydraulics is the operation
of submarines. Inside a submarine, between the outer
skin and the pressure hull, are several tanks of various
design and purpose. These tanks control the total weight
of the ship, allowing it to submerge or surface. They also
control the trim or balance, fore and aft, of the
submarine. The main ballast tanks have the primary
function of either destroying or restoring positive
buoyancy to the submarine. Allowing air to escape
through hydraulically operated vents at the top of the
tanks lets seawater enter through the flood ports at the
bottom to replace the air. For the sub to regain positive
buoyancy, the tanks are “blown” free of seawater with
10-8
