Hydraulics

Question 1

Three possible contaminants?
Causes of these ?
How are they prevented from affecting the system?

Answer 1

a) Three possible contaminants?
Water
Air
Wear Products
b) Causes of these?
Water through a heat exchanger or condensation, free flowing water is bad as it can lead to
rust and boiling
Wear Products from pumps and motors
Air from the suction side of a pump or from undissolved air, pressure changes that compress
air
c) Explain how they are prevented from affecting the system?
Wear Products - Filters from commissioning and then flushing accordingly
Water - Checking oil regularly onboard and via a lab
Air - Checking system pipe work

Question 2

Water in a hrdaulic system?
Possible causes?
consequences?
Action taken if suspected?

Answer 2

a) Possible sources?
As above
b) Consequences?
Corrosion - Rust in the tanks and in the system which can cause seizure and blocked filters
Chemical depletion - Includes additive depletion, oxidation, unwanted reactions which can
form sludges, acids or even alcohols
c) Actions taken should it be suspected?
If suspected best to send away an analysis immediately to get third party confirmation. Then
would look at all the root sources of water in the system, coolers, breathers or tanks and look
back at the logs to when ta top up was made and that the correct top up was made. Try
remove all water firstly.
Can put a coalesce filter or even a portable centrifugal filter than can be hooked up into the
line and circulate the hydraulic oil to remove the level of water to get it to an acceptable level.

Question 3

5 Properties of Hydraulic fluid to fulfil its purpose? And why each of these is important?

Answer 3

Stable - over a range of operating conditions (properties do not change)
Non corrosive - to the various materials used in the system
Good Lubrication - Qualities to reduce friction
Leakages - no impact on the surrounding environment
Low Compressibility - Power can be transferred without delay
Anti-Oxidation Properties - Fluid characteristics should not change when in contact with air
High Flashpoint - to reduce the possibility of fire

Question 4

Windlass that is hydraulically operated, by a variable displacement motor.
Effect of changing the flow of hydraulic oil?
The displacement of the motor?

Answer 4

a) Effect of changing the flow of hydraulic oil
By increasing the flow rate of the pump, the pump will be able to meet the increasing load
from the system and develop the pressure required to maintain operation. So as the load
increases on the windlass the flow rate can be adjusted/maintained to meet the load and
ensure that the windlass can lift the anchor. Can also change the speed.
b) The displacement of the motor
The displacement of the motor in this case can alter the direction of the flow of the oil and
therefore direction of the windlass. It can also offer proportional speed control due to the
amount the swash plate is moved from the neutral position.

Question 5

With the aid of a sketch, two methods of controlling the speed of a hydraulic motor?

Answer 5

We can look at a variety of options here such as a variable delivery pump, such as the swash plate
design. The angle of the swash play both alters the direction but the speed of the motor due to the
increase / decrease of fluid passing through the system
We can also look at the option of utilising flow control valves i.e. variable orifices that will control
the rate of flow through to the motor Air flow control valves operate in the same basic way the
orifices do above, it does however use control air to pneumatically operate a flow valve
Another option, less hydraulically centred, is that of using a frequency drive for the electrical motor
driving the pump. This would allow for a very fine degree of control
See which systems work best for you and base the drawing around this noting that for a 10 mark
question it is normal for 4x marks to be for the diagram and 6x marks for the description –basic “air
flow control valve” drawing on the next slide

Question 6

Hydraulic cylinder operating a safety barrier, explain the consequences of the following?
Dirt in the Hydraulic Oil?
Orifices adjusted to be too large?

Answer 6

a) Dirt in the Hydraulic Oil
The two blocks that are attached to the piston assembly are check and variable orifice valves
which are fine needle valve assemblies. If dirt clogs these up then then there would be no
operation of the barrier arm. Further more the dirt may clog up the relief valve which may
cause it to jam and not open or open to early.
b) Orifices adjusted to be too large
Purpose is to control the flow and hence speed of which the barrier arm will open/closing.
If the orifices are open to large it could be out of the controllable range and speed of
operation will be extremely quick
The consequences are of course safety related also may see premature failure.