Even though certain oils may be satisfactorily
purified at operating temperatures, a greater degree of
purification generally results if the oil is heated to a
higher temperature. To do this, the oil is passed through
a heater where the proper temperature is obtained before
the oil enters the purifier bowl.
Oils used in naval ships maybe heated to specified
temperatures without adverse effects. However,
prolonged heating at higher temperatures is not
recommended because of the tendency of such oils to
oxidize. Oxidation results in rapid deterioration.
Generally, heat oil to produce a viscosity of
approximately 90 seconds Saybolt universal (90 SSU).
You should NEVER increase the pressure above
normal to force a high-viscosity oil through the purifier.
Instead, decrease the viscosity by heating the oil. Using
excess pressure to force oil through the purifier results
in less efficient purification. On the other hand, reducing
the pressure at which the oil is forced into the purifier
increases the length of time the oil is under the influence
of centrifugal force and results in improved purification.
To make sure that the oil discharged from a purifier
is free of water, dirt, and sludge, you need to use the
proper size discharge ring (ring dam). The size of the
discharge ring depends on the specific gravity of the oil
being purified. All discharge rings have the same outside
diameter; but, they have inside diameters of different
The information in this TRAMAN on purifiers is
general, and it applies to both types of purifiers. Before
you operate a specific purifier, refer to the specific
operating procedures contained in the instructions that
come with the unit.
Hydraulic units drive or control steering gears,
windlasses, winches, capstans, airplane cranes,
ammunition hoists, and distant control valves. In this
part of the chapter, you will learn about some of the
hydraulic units that will concern you.
The electrohydraulic type of drive operates several
different kinds of machinery better than other types of
drives. Here are some of the advantages of
l Tubing, which can readily transmit fluids around
corners, conducts the liquid which transmits the
force. Tubing requires very little space.
The machinery operates at variable speeds.
Operating speed can be closely controlled from
minimum to maximum limits.
The controls can be shifted from no load to full
load rapidly without damage to machinery.
An electrohydraulic speed gear is frequently used
in electrohydraulic applications. Different variations of
the basic design are used for specific applications, but
the operating principles remain the same. Basically, the
unit consists of an electric motor-driven hydraulic pump
(A-end) and a hydraulic motor (B-end).
The B-end (fig. 10-37) is already on stroke and is
rotated by the hydraulic force of the oil acting on the
pistons. Movement of the pistons A-end is controlled
by a tilt box (also called a swash plate) in which the
socket ring is mounted, as shown in part A of figure
The length of piston movement, one way or the
other, is controlled by movement of the tilt box and by
the amount of angle at which the tilt box is placed. The
length of the piston movement controls the amount of
fluid flow. When the drive motor is energized, the A-end
is always in motion. However, with the tilt box in a
neutral or vertical position, there is no reciprocating
motion of the pistons. Therefore, no oil is pumped to the
B-end. Any movement of the tilt box, no matter how
slight, causes pumping action to start. This causes
immediate action in the B-end because force is
transmitted by the hydraulic fluid.
When you need reciprocating motion, such as in a
steering gear, the B-end is replaced by a piston or ram.
The force of the hydraulic fluid causes the movement of
the piston or ram. The tilt box in the A-end is controlled
locally (as on the anchor windlass) or remotely (as on
the steering gear).
The steering gear transmits power from the steering
engine to the rudder stock. The steering gear frequently
includes the driving engine and the transmitting
Many different designs of steering gear are in use,
and they all operate on the same principle. One type of