Hydraulics - Seafish

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PROPERTIES OF HYDRAULIC OILS
The use of clean, high quality fluid is the first step in achieving
efficient and reliable operation of hydraulic systems.
The most common fluid used in hydraulic systems is oil. This is
not just any oil that happens to be available, but an oil which has
particular properties.
Oil is a lubricant, which means that all moving components are
being lubricated as they work and this keeps them moving freely.
It also reduces wear on the parts to a minimum and prolongs the
working life of the components.
As well as being a lubricant the oil must:
• transmit power,
• seal the working clearances,
• act as a cooling agent and remove heat from the working
parts.
Oil is virtually incompressible which means that action is almost
instantaneous when a pump is started, or when a valve operates.
But this is only true if there is no air entrained in the oil or air
pockets trapped in the system.
You will no doubt be aware that it is necessary to bleed the air
from the braking system of a car if the brakes are to be properly
effective.
Also to give good action and to provide proper lubrication and
sealing of clearances and glands, the oil must have the correct
range of viscosity.
Viscosity of Oils
The viscosity of an oil is a measure of its resistance to flow and
varies with its temperature.
When temperatures are low the oil
order to lubricate all the rubbing surfaces.
must be able to flow freely in
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