"We will soon need to choose a new oil for one of our hydraulic systems but are concerned about the mixing of hydraulic oils. Do we have reason for concern?"
There are dozens of additives available for use when blending hydraulic oils. Some anti-foam additives, for example, may prevent the buildup of foam on the oil's surface, but at the same time may actually retard the release of air trapped in the bulk oil. As a result, the mixing of hydraulic oils with different anti‑foam agents may actually increase the foaming of the oil.
Some hydraulic oils may be blended to allow water to mix or emulsify with the oil. On the other hand, some oils are formulated to ensure that the water separates from the oil. Therefore, the mixing of hydraulic oils with differing water separation characteristics may cause a reduction in emulsification characteristics or eliminate these characteristics altogether, thereby causing undesirable operating conditions.
Hydraulic oils should be chosen based upon the equipment manufacturer's specifications, keeping in mind the temperature range in which the equipment is to be operated. Occasionally, the manufacturer's specifications may recommend an oil that may not provide the necessary protection due to unique or unusual operation conditions. If these situations occur, detailed consultations with the equipment manufacturer and oil supplier, in cooperation with an independent oil analysis laboratory, are recommended.
Generally speaking, however, it is suggested that top-quality hydraulic lubricants should meet the following requirements.
In addition, hydraulic fluids must be maintained in order to ensure their long life and reliability. Some recommendations include: