Often, users of hydraulic fluid will confuse a chemical analysis with a complete fluid analysis, which provides particle count of contaminants, amounts of water, and more. Oil samples that are sent off to a lab without specific instructions will return with valuable data but not all the data points you require. In most cases, the majority of labs that deal with hydraulic fluid contamination must be specifically tasked with providing particle count tests. It’s a separate testing procedure that usually includes an extra fee.
A chemical analysis is very scientific in one sense, where you must have a recipe of the original oil that you used. It determines what type of oil you are using — mineral-based, synthetic, water-based, etc. — along with any other additives used. This helps you know what types of deviations you’re having. In hydraulic systems — unlike engines or those types of applications where you have high internal combustions and the oil breaks down — it is recommended that you do a chemical analysis annually to help predict baseline data and understand what you’re starting with. If at some point during the year, you shift and change your oil supplier, then their recipe is going to mix with the other one unless you’re doing a complete change-out. As a result, a new analysis should be done.
In addition to having a scientific report of your hydraulic fluid’s chemical analysis, it is recommended you also test for additional data, such as particle counts, viscosity index, water content and more. These very specific tests conducted on hydraulic oil give you a bigger picture over just a chemical analysis. These samples should be taken while the system is operating, and from a line with active flows. This gives you a true look at your fluid’s makeup and all that may be in it.