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Varnish Issues in Hydraulic Fluid ben lee

10 Minute Guide to Varnish Issues in Hydraulic Fluid 

Oxidation and static discharge have a lot to answer for. Did you know that they cause almost all (85%) of hydraulic component related failures?

In this post we’re going to cover a few important points that you need to know that will help to cut the expense and downtime caused by these two engineering problem culprits.

The root of the problem

At the core of the varnish issue is obviously the fact that it builds up at all, if it wasn’t there – it wouldn’t be causing such damage and system performance degradation. The issues start when there are insoluble contaminants in the system. These are far too small for filters to trap them, and cannot even be detected during the particle counting process. However, once these build up they begin to form tar and varnish.

If you’re wondering where these insoluble contaminants come from, then read on. Unfortunately it’s a fact that this occurs throughout the entire system. When static discharge occurs, it mixes with water and oxygen and the process of oxidation commences. The result is insoluble contaminants in the form of tar and varnish.

Why does static discharge happen?

Static discharge comes about in the form of sparks that are caused by friction with the oil. With the sparks at a temperature of 10,000° C – the oil gets cooked. This heat is hotter than the sun, no joke! The cooked oil then turns into varnish and that goes around the system and causes mayhem by sticking onto the internal surfaces. As time passes, the hard particles will stick to the varnish, creating a surface similar to sandpaper. Sticky valves, reduced performance and you’re headed towards system failure if things don’t improve fast.

If that isn’t enough to be concerned about, the varnish has a high acid content. This can breakdown seals and o-rings causing them to become brittle. The sticky nature of the varnish then goes onto attract larger particles and its all downhill from here.

However, there are some things you can do about varnish. For example, you can eliminate it before it starts to create all these problems.

Let’s understand what you can do to ensure that your oil is clean.

Too much heat in the ‘kitchen’

There are four heat sources within the typical hydraulic system:

Friction — all that metal together doesn’t help anything.. Very high temperatures can be generated - up to between 180° and 450° C.
Adiabatic compression — with the result being temperatures between 600° and 900°C.
Dark stream spark discharge — although you won’t see the spark itself, temps of up to 5000° and 10,000° C can be generated.
Full spark discharge — along with the flash, but for just a nano-second – temps between 10,000° to 20,000° C.

Sparks can be caused by the high pressure and temperature, in addition to friction with the oil. This friction can cause spark discharge without adding in the high pressure and the temperature.

Spark discharge in a filter

Spark discharge on filters occurs on the downstream side. This is because it is usually situated between the pleated edges and grounded centre core. Spark discharges also occur elsewhere including in reservoirs. Oil to air friction can also occur if air has a chance to mix, that’s why it’s important to bring return oil pipes into oil.

Oxidation by-products
Varnish can be left in any area where oil touches a surface. Take a look in your reservoir to check whether you can find it throughout the system. No matter what type of hydraulic fluid is used, varnish will occur.

The electrostatic solution

Although traditionally oil cleaning has been done through the use of filtration, strainers and centrifuges, these methods don’t really work when it comes to sub-micron sized contaminants such as oil that has just been ‘cooked’. These particles can only be removed through electrostatic oil cleaning.

Although electrostatic oil cleaners are so effective, they should not be relied upon as a method to remove larger particles. They are really only effective on soft contaminants that will go on to create varnish if left unchecked.  However, the benefits are greater efficiency, less downtime, less system flushes and cost reduction. There won’t be so much need to replace seals, o-rings and filters as there’ll be less varnish on the ‘loose’.

As a result of an effective clean up, you can expect to have just 15% of your failures related to varnish and oxidation issues instead of 85%. Well worth the effort! 

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