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Hydraulic Systems: Water and Oil Don’t Mix ben lee

If you’ve been in the hydraulic industry for some time, there’s no doubt that at some point you will have seen cloudy oil. This is what happens when there is contamination with water above the oil’s level of saturation. The definition of a saturation level is how much water can dissolve in oil – for mineral hydraulic oil this will typically be around the 200 to 300 ppm at 68 F or 20 C.

As an aside, something worth knowing is that bearing life can be increased by almost 150% if water concentration is reduced to just 25 ppm.

The more water in the oil, the more issues you’re going to face. One of our engineers recently witnessed oil that so was incredibly cloudy because it had over 10,000 ppm of water in it which actually made it more than 1% water!


Here’s what happens when there is water in hydraulic fluid:


·         Either depletes or reacts with additives to form by-products that can corrode some metals

·         Clogs filters by reducing filterability

·         Increases ability of air entrainment

·         The likelihood of cavitation increases

·         Lubricating film-strength is reduced leading to corrosion and wear vulnerability

It’s also possible to spawn bacteria with water present in oil.


Measuring and Removing Water

How can you measure how much oil and how much water you have in your hydraulic fluid?


The test that is considered to be the standard laboratory method is the Karl Fischer Volumetric Regent Method which others may know simply as the Karl Fischer test. Another method sometimes used is the FTIR or Fourier transform infrared spectroscopy test. However, this is a test that can only really be considered effective with oil and water mixes that are greater than 1000 ppm of water. If you’re serious about measuring water contamination, we recommend that you go with the Karl Fischer.


Now that you know that there are some very unpleasant side effects when there is water in your oil, what are you options with regards to removing it? If you’ve got a system that has only a small volume of oil, then you may opt to change the oil. This option will most likely prove to be the most cost effective approach. For larger oil volumes, it’s best to use filters built for water removal when there is small amounts of water involved.


Water removal filters come in two types, polymeric and coalescing. The former works by using chemicals that attract water. They absorb water drops and retain them permanently. Whereas coalescing filters collect the water and put it into a collector which is drained once in a while. Water that has been dissolved will not be collected by either filter types.


Another approach to collect water is the headspace dehumidification approach. This uses the reservoir’s headspace to circulate and dehumidify the air. Water will then migrate to the headspace where it is removed by a dehumidifier.


Headspace flush is another approach that is similar to the previous method, except that it is collected by a small flow of dry compressed air that is flushed through the headspace. The dry air will pick up the water.


One more approach is to use a variation on the headspace flush by using a hygroscopic breather and then connecting a vacuum pump. This approach is reliant on a spare port located on the top of the reservoir, as distant from the breather as possible. This method does not need a source of dry compressed air.


We are in the business of supplying mobile power packs for hydraulic systems. If you want to know more about our products, browse through our hydraulic unit product pages or call us for a no obligation chat. 

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