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Hydraulic oil Compressibility: What is it and what are the risks?

Before we find out about oil compressibility, it is also important to first understand about the definition of compressibility and its fundamentals. So without any delay, let’s get straight to the topic.

Oil Compressibility:

It refers to the relative change in oil volume per unit change in pressure. It is a key source of energy for the flow of fluid in a reservoir. After a certain pressure, the oil becomes single-phase liquid comprising oil and dissolved gas. This is also commonly referred to as an under saturated condition.

If we go by the exact numbers, experts suggest a rule of thumb and it is applicable universally. It says that oil will compress roughly 0.5% for every 1000 psi exerted. Now having said that, for most of the applications you can consider it incompressible or negligible. It significantly changes subject to temperature, pressure, molecular structure, gas and also the elasticity of the hydraulic system.

It is widely known that compressibility of the oil causes some problems in the long run. It may also hinder the performance of the tools and machines it is applied to. That’s why it is imperative to know about oil compressibility. You should have greater insights about the aberrations and fluctuations. When you are aware of the factors that cause the changes, you will be able to control the outcome.

Did you know that hydraulic oils are also compressible?

What it means is – there are likely to be problems in the hydraulic systems. According to experts, changes in temperature in the hydraulic oil and formation of bubbles vastly influence the compressibility. What it does is – it leads to uncontrolled decompression and other types of related compressibility problems.

What all factors affect compressibility of hydraulic oil?

Yes, there are 4 key factors which may influence the performance. Those factors are

● Thermal expansion
● System design
● Formation of air bubbles

What we often don’t realize is that hydraulic compressibility can also cause a number of risks. Don’t worry! Here we will have a detailed look and help you understand how it affects. Here are some of the terms which are most commonly used to determine the risks and effects:

First, thermal expansion of hydraulic oils; we all know that the volume of hydraulic oil changes with respect to pressure and also the varying temperature. As the temperature goes up, the density of the hydraulic oil decreases which leads to volume increase. The amount of expansion is denoted as the coefficient of thermal expansion. This degree of change is represented with (α).

This coefficient is generally the ratio of the relative change in volume because of change in temperature. It may not seem significant at first, but can play a crucial role in determining the output of the hydraulic system.
System design also affects compressibility – Simply put, the elasticity of the system contributes to the overall compressibility. It affects each component of the hydraulic system.

Air Bubbles Affect Compressibility – Air bubbles are present in the hydraulic fluid which leads to an increase of compressibility. In simpler words, this dissolved air reduces the bulk modulus of the mineral oils and hence there is decrease in resistance to compression. It happens in particularly low pressures when the fluid is pressurized and the air gets compressed and has low effect on compressibility.

Are There Any Negative Effects Of Compressibility?

It is believed generally that the hydraulic fluids are incompressible. But the mineral oils are compressible and it may lead to problems in the hydraulic systems. These problems mainly are power loss, efficiency loss, cavitation or metal fracture, corrosion and more. This compression of hydraulic fluids often results in storage of extra energy.

And if decompression is not brought under control, then this stored energy gets released. It results in unnecessary noise, serious damage, and added stress to the hydraulic components. Besides this there are other effects too that add up. Increase or decrease in volume due to inappropriate use of oils also affect compressibility.

But now the question arises how we avoid such a high compressibility in hydraulic oil systems. So the main requirement to bring down compressibility is met by keeping the hydraulic fluid free from entrained air.

Conclusion – Experts advise that you must use good quality oils and fluids which are manufactured by top brands. Finding a perfect hydraulic fluid that comes with proper stiffness may prove to be an impossible task.

There are always limitations but you can take care of it using your knowledge or by seeking advice from experts. For better response and optimum performance, it is more important than ever to carefully consider operational effects of the fluid compressibility in your hydraulic equipment.

Make sure you find the right hydraulic equipment and system. It is advisable to choose the right set of oils and fluids which are of highest standard. This is why you should buy the oil and fluids from top quality brands.

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  1. Thankyou this blog helps me alot.

  2. This is a really good tip particularly to those new to the blogosphere.

    Brief but very accurate information? Thanks for sharing this one.

    A must read article!