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What is Hydraulic Oil Compressibility and its Risks?

Hydraulic fluids are used all around us. In almost any industry, hydraulic oils form an essential component, helping to lift, turn or move. However, what makes it work so well, and by understanding it, can we make sure that we use suitable hydraulic fluids?

Let us look at Oil Compressibility:

Oil compressibility refers to the relative change in oil volume per unit pressure change. It is an essential energy source for maintaining the flow in a reservoir. After a certain pressure, the oil transforms into a single-phase liquid composed of oil and dissolved gas. This is called an under-saturated state.

Based on research, experts recommend a universal rule of thumb. According to the data, oil compresses by around 0.5 percent for every 1000 psi applied. It is incompressible or insignificant for most applications. It changes significantly depending on pressure, gas, temperature, and hydraulic system elasticity.

In the long run, oil’s compressibility might present some issues. It may also impair the performance of the tools and machinery on which it is applied. That is why understanding oil compressibility is critical. It would be helpful for users to understand the anomalies and variations better. When you know the factors that cause the changes, you can control the outcome.

Are hydraulic oils compressible?

Hydraulic systems can have problems. Many specialists believe the temperature of the oil and the formation of bubbles can significantly impact the oil’s compressibility. It can cause uncontrolled decompression and various forms of compressibility issues.

The factors affecting the compressibility-

  • Thermal expansion
  • System design
  • Air bubble formation.

We frequently fail to see that hydraulic compressibility may also pose various problems. Do not be concerned! Here are some of the most commonly used terms in risk and effect estimation:

Thermal expansion of hydraulic oils; The volume of hydraulic oil varies with pressure and temperature. As the temperature rises, hydraulic oil increases in volume as the thickness decreases. Here the degree of change is indicated by (α). This coefficient is commonly defined as the ratio of the relative change in volume due to temperature change. Initially, it may not appear relevant, but it can play a critical role in the hydraulic system’s output.

Effect of system design – The system’s structure and elasticity add to total compressibility. It has an impact on every component of the hydraulic system.

Effect of Air Bubbles: Air bubbles will form if air is accidentally introduced into the hydraulic system. The presence of air bubbles increases compressibility. Simply put, the dissolved air decreases the bulk modulus of the mineral oils, resulting in a decrease in compression resistance. Oxidation can also occur when air is present.

Are there any Negative Effects Of Oil Compressibility?

Hydraulic fluids are thought to be incompressible. However, mineral oils are, to some extent, compressible, which can cause issues in hydraulic systems. These problems include power loss, efficiency loss, cavitation or metal fracture, corrosion, etc. Hydraulic fluid compression frequently results in the storage of excess energy. Assume that the decompression is uncontrolled and that the stored energy is released. In that case, it will cause extra noise, severe damage, and additional stress on the hydraulic components. Besides that, several other issues pile up. Compressibility is also affected by volume changes caused by improper oil usage. Proper maintenance can mitigate this.

However, we must now ask how to prevent such high compressibility in hydraulic oil systems. The main requirement to reduce compressibility is met by keeping the hydraulic fluid free from entrained air.


Experts recommend using high-quality oils and fluids made by reputable companies. Here you can have confidence in GRENVO. We are a member of the SGL family with over 60 years of heritage in the oil business and are trusted globally.

There will always be restrictions, but you can deal with them by applying your expertise and obtaining guidance from the OEM. It is more critical than ever to carefully analyze the operational impacts of fluid compressibility in your hydraulic equipment for improved reaction and maximum performance.

GRENVO, the brand of choice for your lubrication needs

Grenvo manufactures outstanding quality hydraulic oils that are developed for meeting lubrication needs. Our hydraulic oils are made from high-quality oils and additives; we manufacture anti-wear, non-zinc, and ashless hydraulic oils for use in industrial and mobile service applications. GRENVO helps extend the life of your equipment and reduces the cost of ownership.

Discover GRENVO’s world-class hydraulic oil range for your fleet-

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