2.2.3 HYDRAULIC DRIVE UNIT
The hydraulic drive unit should be mounted clear
of spray and the possibility of immersion in water.
It should be located as near as possible to the
hydraulic steering cylinder. It is important to bolt
the hydraulic drive unit securely to a substantial
member to avoid any possibility of vibration that
could damage the inter-connecting pipework.
There are three basic types of hydraulic
steering system, and these are illustrated in
(Fig. 26). Typical connection points for the drive
unit are shown in each case.
In all cases it is
strongly recommended that the steering gear
manufacturer be consulted.
The drive unit valve
block is tapped
BSP
to.accept suitable pipe
fittings and Dowty sealing washers are supplied.
Minimisation of hydraulic fluid loss during
connection of the drive until will help to reduce
the time and effort required later to bleed the
system of trapped air. Absolute cleanliness is
essential since even the smallest particle of
foreign matter could interfere with the correct
function of precision check valves in the steering
system.
When the installation has been completed the
hydraulic pump may be operated by switching the
control unit to ‘Auto’ and operating the
0” and
course change buttons. Greater motor
movements will be obtained if the gain control on
the course computer is set to No. 6 and the
rudder control set to maximum.
Two Line System
The hydraulic steering system should be bled
according to the manufacturers instructions. From
time to time during the bleeding process the drive
unit should be run in both directions to clear
trapped air from the pump and inter-connecting
pipe work.
If air is left in the system the steering will feel
spongy particularly when the wheel is rotated to
the
position. Trapped air will severely
impair correct operation of the autopilot and the
steering system and must be removed.
During the installation of the system it has not
been necessary to keep track of the connection
sense to the hydraulic steering circuit since
operating sense of the autopilot can be corrected
if necessary by reversing the polarity of the pump
drive motor connections (see section 3.3.1).
CONNECTION OF HYDRAULIC
LINES TO PUMP
, DOWTY SEAL
,DOWTY SEAL
Assembly for
Line Fitting
A D A P T O R
Assembly for
NPT
Line Fitting
Two Line
P r e s s u r i s e d S y s t e m
-RESERVOIR LINE
Three Line System
RESERVOIR LINE
