The importance of oil sampling and the best practice to employ

13 April, 2017

It is a well-known statistic that over 80% of all hydraulic system failures are caused by contamination. The best way to protect against machine failure is to put a fluid management strategy in place, which includes regular oil sampling and analysis, along with the necessary remedial processes of oil filtration and system flushing.

How often should I take samples?

When to sample and what results to look out for will be dependent on the system that you are taking the sample from; each will have its own target cleanliness level. As a guideline, we would recommend samples are taken once a month and on each delivery of new oil.

What is the correct way to take a sample?

Firstly, ensure your sampling equipment and container are clean and dry for each sample taken. The machine should be running and at normal operating temperatures and load pressures.

Always sample upstream of filters and downstream of machine components such as bearings, gears, cylinders etc. For applications that are running regularly at high pressures, secondary sampling points around components are recommended, enabling accurate diagnosis of where the build-up of particulate contamination is.

What should I look out for when looking at the cleanliness of oil?

Visual clarity does not always mean that the oil is within specification. The human eye cannot see particles below 40µm and you cannot always see water.

As particulate contamination is one of the main reasons for system failure, monitoring the level of hard contaminants is vital. Checking the ISO code is in line with your systems’ required cleanliness is the first step.

It is also important to remember to check for water contamination in the oil. Water can cause a whole host of issues, from oxidisation and component rusting, to depleting additive packages. Oil that is contaminated with water often has a milky appearance. The majority of oils have a maximum allowable water content level and problems start to occur over this level.

What analysis method should I use?

There are three main methods for establishing oil cleanliness and analysis with their own benefits:

A sample is sent to a lab who uses a sophisticated spectrometer to analyse the fluid, allowing identification of wear metals, oil additives, solid contaminants, dirt and water.

Laser particle counters and water content sensors can help understand an oils condition in real-time, giving live ISO cleanliness and water content levels in minutes.

Patch testing enables instant visual analysis, through an optical microscope, of the major wear elements including metals, silica, fibres, plastics etc.

What does the ISO code mean?

ISO 4406:1999 is an internationally recognised method of measuring particulate in a given oil or lubricant sample. The code is measured in microns: 4-micron, 6-micron and 14-micron. Each number displays the contaminant level for the specific particle size. Every time this number increases the particulate contamination is gradually degrading the oil. The following is an example code of 18/16/13:

• 18 – represents a range or count of particulate from 1300 – 2500 at 4 micron and greater in size.

• 16 – represents a range or count of particulate from 320 – 640 at 6 micron and greater in size.

• 13 – represents a range or count of particulate from 40 – 80 at 14 micron and greater in size.

How is water measured?

Hydraulic oils will have a specified level of water that is permissible. This is usually measured in either parts per million (PPM) or relative humidity (RH). One ppm is equivalent to 1 milligram of water per litre of oil (mg/l).

Relative Humidity is expressed as a percentage. 100% RH equates to the maximum amount of absorbed water a given oil can hold before it becomes saturated and free water forms.

Target water content levels should be no higher than 100ppm. To obtain accurate water content readings, you can use a Karl Fischer Titration method, water sensors or independent laboratory analysis.

Once the level of solid and water contamination is established the appropriate remedial actions can be undertaken. For advice on analysis, reading results or filtration best practice, please contact one of the Filtertechnik team.

Free ‘First Aid For Oils’ booklet available

This article has been compiled from content contained within Filtertechnik’s oil cleanliness guide titled ‘First Aid For Oils’. The free guide can be downloaded from www.filtertechnik.co.uk/downloads or a hard copy can be sent in the post. For a copy, call 0115 9003 600 or email sales@filtertechnik.co.uk.

www.filtertechnik.co.uk

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