Hydraulic fluid requirements and characteristics

When I have entered in my industrial life , I have observed that approximate every machine is dependent on hydraulic system . I was very interested to gain knowledge about the hydraulic function and maintenance of hydraulic system.

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We have studied above the various tasks for hydraulic fluid and in order to complete the above tasks successfully, hydraulic oil must have following properties under the desired operating situation.
Let us understand the characteristic of one standard hydraulic fluid
1. Low flammability
2. lowest possible density
3. good material compatibility
4. Minimal compressibility
5. Good ageing stability
6. Viscosity not too much low
7. Should be able to form lubricating film
8. Good viscosity-temperature properties
9. Good viscosity-pressure properties
There are some more requirements that hydraulic oil must fulfill and these are as mentioned below
1. Air release
2. Resistance against cold
3. Non frothing
4. Water separable
5. Corrosion and wear protection
Viscosity is very important factor for selecting the desired hydraulic oil, as viscosity play lead role during selection of hydraulic oil hence i want to give brief concept of viscosity so that we may understand this blog clearly.

Viscosity determine the internal friction of moving fluid, it indicates the resistance to flow.
In simple way we may say viscosity provides the information that how easily one liquid could be drained or poured. Let us consider two liquid such as honey and water now we may understand that honey will take much more time for draining or pouring, while water will not take too much time for draining or pouring.

### We need to know why?

We will read the concept of viscosity. Honey is quite viscous as compared to water that's why honey will take much more time for draining or pouring.

We use kinematic viscosity in our engineering calculations. Ball viscometer is used for determining the kinematic viscosity.

I will post one separate blog, where we will read how we determine the kinematic viscosity by Ball viscometer.

We have already stated above that viscosity play important role in hydraulic oil selection for one hydraulic system. Let us understand the various hydraulic oil grades and their viscosity range at specified temperature i.e. at 40C.

When we go for the application of hydraulic oil, it is very important for considering their viscosity temperature characteristics, as we know that viscosity of any type of hydraulic oil varies with variation in temperature. These variations are displayed in the viscosity-temperature curve as mentioned below.
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