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Posted on : Friday 22nd May 2020 01:33 PM

Oil Density Analysis: The When and Why

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The density attribute is extremely important for oil analysis in predictive maintenance as it plays a key role in the lubricant performance and therefore in the performance of the machinery. See in the following post how this occurs and the importance of oil density analysis to ensure the functionality of your systems. 

What is the analysis of oil density and how important is it?

Density is a key property of a fluid and is given by the ratio of its specific mass to a known volume (d = m / V). The water, reference standard, has a density of 1, 000 kg / m³ by definition. Already the oils vary between 700 kg / m³ and 950 kg / m³. That is why most oils float in water: they are less dense than it. Some Group IV base oils of the API system, however, may be more dense and sink into the water.

That is why, when there are excess moisture problems in your lubrication system, water decants at the bottom of the tank and can be drained first when the lid or valve is opened. In the case of denser oils, such as those in Group IV, the opposite occurs, and water floats on the lubricant.

For the API classification, however, the density measure is made differently, using an inverse scale comparison. In this system, the value 10 is assigned to water, and any fluid having a higher value than it has a density less than water and will float therein; Anything less than 10 will be heavier and will sink.

An important characteristic of the density is that it varies according to the temperature of the oil in reverse: the higher the temperature, the lower the density.

The density value of a fluid is used in calculations of viscosity, the most important property of a lubricant. This is therefore the main reason for performing the oil density analysis: without such information, it will not be possible to determine the viscosity.

How does density affect lubricants and machines?

As mentioned, to know the viscosity of a fluid, one must first know its density. Knowing this value, we can verify that, with increasing density of a lubricant, the fluid becomes thicker. One of the consequences of this is that any particles dissolved in this fluid will take longer to decant.

In relation to hydraulic systems, this information is extremely important as it means that the mechanism will be exposed to particulate contamination for longer. Hydraulic assemblies are very sensitive to any type of contamination, and longer residence time of these suspended particles can cause problems such as cavitation, corrosion and clogging of the valves by formation of sludge in the oil.

On the other hand, high density fluids can help control contamination. In this case, the longer period of flotation in the liquid facilitates the removal of particles through filtration or other mechanisms, aiding the process of cleaning the assembly.

In this context, hydraulic pumps are the equipment that suffer most from changes in density. Among the problems that can be caused are:

  1. Increased cavitation propensity at pump suction and outlet ports.
  2. Increased pumping power (consumption of more energy, causing engine wear).
  3. Increased stress in the pumping elements.
  4. Commitment of pumping capacity due to increased fluid inertia (oil does not flow as it should).

The erosive potential of the fluid also increases with increasing density. At points in the system where there is great turbulence (or great velocity of fluid passage). That is, the greater the density at locations where the fluid has high velocity, the greater the likelihood that the fluid will erode pipelines, valves, or any other surfaces in its path.

Other contaminants such as air and water in the oil will also be affected by the change in lubricant density. In fact, changes in oil density, on the other hand, can indicate air and water contamination, since these two contaminants affect this property. Changes in said property also indicate oxidation. In this case, the density rises with the advancement of the oxidative process. All this information can be verified more clearly once the analysis of the oil density is carried out.

Benefits of Oil Density Analysis for Operation

Since it is a function of temperature, variation in oil density may be indicating overheating in the machine parts. In this sense, the analysis of the oil density must be done whenever there is observation in the field of changes in the performance of hydraulic pumps or overwork in them. That is, if you noticed that the pumps are wasting more energy, it may be that the oil density is changed. If so, it is necessary to perform different types of oil analysis in order to detect exactly what the problem is.

This indication is made because the pumps are designed for a specific type of oil density. Therefore, as the density changes, loss of pumping efficiency occurs, causing production losses and increasing costs. Performing oil density analysis, in this case, is crucial.

In short, density plays a key role in lubricant performance and machine performance, especially in the case of hydraulic system pumps. This is because these equipments are designed according to the oil density to be used in the system, and any change in this property will compromise its performance.

Similarly, higher densities in the oil will indicate longer residence time of the suspended particles. On the one hand, this can be a problem, since it exposes the system to the harmful presence of contaminants. On the other hand, it can help to clean the set for the same reason. In addition, density changes, and is also altered by the presence of air and water, contaminants that can cause significant damage to equipment, such as corrosion, cavitation and valve clogging because of the formation of sludge.

Take the oil density analysis quotation and find out how soon your oils are suitable for optimizing your production process.


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