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  • Anshuman Agrawal

Functions of hydraulic oil and the reasons of its contamination

Updated: Jul 16

There are four basic functions of hydraulic oil:

  1. To act as an energy transmission medium

  2. To Lubricate internal moving parts of components

  3. To act as a heat transfer medium

  4. To seal clearances between moving parts

If any of these functions is impaired, the hydraulic system in the equipment/rigs will not perform as designed. The resulting downtime can cost a lot in Dollar and increase the operating cost for any rig/operations on field.



Proper hydraulic fluid maintenance helps to prevent or reduce breakdown maintenance. This is accomplished through continuous improvement program that minimizes and removes contaminants.

Hydraulic fluid is expected to create a lubricating film to keep precision parts separated. Ideally, the film is thick enough to completely fill the clearance between moving parts. This condition results in low wear rates. When the wear rate is kept low enough, a component is likely to reach its intended life expectancy.


The actual thickness of a lubricating film depends on:

1. fluid viscosity

2. applied load

3. relative speed of the two surfaces

So, if after multiple cycles the oil loses its viscosity or is contaminated. It will lead to addition friction and wear and tear.


What harm will the contaminants make?


If not properly flushed, contaminants from manufacturing and assembly will be left in the system. These contaminants include dust, welding slag, rubber particles from hoses and seals, sand from castings, and metal debris from machined components. Also, when fluid is initially added to the system, contamination is introduced. During system operation, contamination enters through breather caps, worn seals, and other system openings. System operation also generates internal contamination. This occurs as component wear debris and chemical by-products react with component surfaces to generate more contamination.


What are the types & sources of Contamination?


There are basically 4 sources of contamination:

1. Built-in Contamination

2. Natural Contamination

3. Ingressed Contamination

4. Generated Contamination


While the first three types of contamination is self-explanatory, there is the further classification of generation contamination on the basis of how it is generated:

1. Abrasive Wear: Hard particles bridging two moving surfaces, scraping one or both.

2. Cavitation Wear: Restricted inlet flow to pump causes fluid voids that implode causing shocks that break away critical surface material.

3. Fatigue Wear: Particles bridging a clearance cause a surface stress riser that expands into a spall due to repeated stressing of the damaged area.

4. Erosive Wear: Fine particles in a high-speed stream of fluid eat away a metering edge or surface.

5. Adhesive Wear: Loss of oil film allows metal to metal contact between moving surfaces.

6. Corrosive Wear: Water or chemical contamination in the fluid causes rust or a chemical reaction that degrades a surface.


Are contaminants visible with naked eye?


Particle sizes are generally measured on the micrometer scale. One micrometer (or micron) is one-millionth of one meter, or 39 millionths of an inch. The limit of human visibility is approx.. 32μm micrometers. Keep in mind that most damage-causing particles in hydraulic or lubrication systems are smaller than 14μm micrometers. Therefore, they are microscopic and cannot be seen by the unaided eye. To put the sizes in perspective, below are the sizes of some known objects.

Hence filtration of hydraulic oil is of prime importance. Minimac System provides an array of the solution in this regard. What we also do is filter check via our experts for any of your rig/equipment.



At Minimac Systems we offer Flushing Services and Filter Check Services which ensure a clean system including oil tanks and lines. Book an appointment with our technical expert by clicking on https://www.linkedin.com/company/minimacsystemsprivatetlimited or call +91 8975150700



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