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1. Hydraulic Drive Units
Three types of hydraulic drive units are covered, the constant running power pack,
the reversing gear pumps and the type '0' piston pump. The most common cause of
problems is trapped dirt in the valve assemblies between the balls and their seats.
This provides a short circuit path for the oil, which will greatly reduce the pressure
generated to move the steering cylinder. It is important to observe absolute
cleanliness at all times during dismantling and reassembly. If it is necessary to
service the drive units when installed the following points should be observed:-
- Hydraulic pressurised systems must be depressurised before work is started.
- The drive unit should be isolated from the main steering system to minimise fluid
loss.
2. Constant Running Power Pack (Z064, Z065, Z066, Z067)
The constant running hydraulic power pack provides a drive unit for larger vessels
with steering cylinder displacements above 400cc. The power pack motor is switched
independently of the autopilot and runs continuously. When rudder movement is
required, the solenoid valves are energised by the course computer to direct the flow
to the steering cylinder.
The servicing information allows replacement of the solenoid valve assembly,
inspection and cleaning of the check valve and relief valve assembly and seal
replacement. It is not possible to service the pump and filter assembly which are
contained within the reservoir as the reservoir seal requires special assembly
techniques.
2.1 Dismantling and Reassembly
a) To remove the solenoid valve, undo the four caphead bolts securing it to the
manifold. Remove the valve carefully to ensure the 0 ring seals are not lost.
Reassembly is a simple reversal of this procedure.
b) To clean the check valve assembly, unscrew the cartridge and remove it along
with the washer and 0 ring seal. The spring and ball can then be taken out. The seat
and 0 ring will probably remain in position and oil from the reservoir is likely to wash
out any dirt that could have been causing problems. If the check valve assembly is
further dismantled, care must be taken when reassembling to prevent damage to the
0 rings. The best method is to place the 5/ Sin. 0 ring and seat in the manifold and
screw in the cartridge (without the ball or spring) to position the seat within its sealing
ring. The cartridge can then be removed and the ball and spring positioned within the
cartridge. Some grease may be used to retain them whilst the cartridge with its 0 ring
and washer is screwed into position.
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