Most hydraulic systems will work equally well with a variety of different fluids, as long as certain vital parameters are adhered to in terms of temperature ratings, viscosity, etc. However, in addition to your basic fluids there are also options that include extra features such as multigrade properties, detergents, and anti-wear additives. In general, it’s best to stick with the fluids recommended by your equipment manufacturer. However, in certain circumstances it may be beneficial to use a fancier fluid with certain special properties that can improve performance or longevity. Here are some of the key points you need to know about various special properties.
Multigrade oil is useful for applications where you need to operate your hydraulic equipment in a wide range of temperature conditions. A good example might be a piece of mobile equipment that has to handle freezing winter temperatures and sweltering summer ones. The multigrade properties of the oil help to expand the operating temperature range by ensuring that viscosity remains in the desired range regardless of the eternal temperature.
The main drawback of multigrade fluids is that they can create air separation problems, meaning it will be more difficult for any air that gets into the fluid to work its way back out. This is a particular problem in mobile hydraulic systems that typically have small reservoirs that aren’t ideal for de-aeration to start with.
Many fluids have detergents added to them to help prevent contaminants from precipitating out of the fluid and gunking up various hydraulic components. This can be great for component life, but since the contaminants will stay suspended in the fluid rather than settling to the bottom of a reservoir, you must have proper filtration to remove them.
Detergents also have the effect of emulsifying any water that gets into the fluid, which means that the water won’t be able to separate out of the fluid like it would with a more basic oil. This can be problematic because water makes oil age faster and reduces its ability to lubricate. If you have a water incursion problem while using detergents you may end up with corrosion and cavitation problems.
Zinc dialkyl dithiophosphate (ZnDP) is the most commonly used anti-wear additive in hydraulic fluids. It helps to maintain lubrication and is considered especially important for high-pressure, high-performance piston pumps and motors. If you are meant to be using this sort of fluid, the manufacturer will surely recommend it. Otherwise, you may risk chemical reactions that can attack the metals in some hydraulic components. Be sure you are using a newer, stabilized formulation that minimizes this risk as much as possible.