Because it can chemically break down and attack these metals while also reducing filterability. While ZDDP is effective, it may not be optimal when used with certain metals or oil filtration systems. The most common antiwear additive used in engine and hydraulic oil is zinc dialkyl dithiophosphate (ZDDP). The purpose of antiwear additives is to maintain lubrication under boundary conditions. When to use antiwear (AW) hydraulic fluid When selecting a high VI or multigrade fluid, a good guideline is that the hydraulic component manufacturers’ minimum permissible viscosity values should be increased by 30 percent to compensate for VI improver sheardown. The high shear rates and turbulent flow conditions often present in hydraulic systems destroy the molecular bonds of the VI improvers over time, resulting in loss of viscosity. This is not ideal, particularly in mobile hydraulic systems which have a small reservoir with poor deaeration characteristics. The viscosity index (VI) improvers used to make multigrade oils can have a negative effect on the air separation properties of the oil. This means that under certain conditions, the use of a multigrade can reduce the power consumption of the hydraulic system.įor mobile hydraulic equipment users, this translates to reduced fuel consumption.īut, as we said, multigrade fluids are not always ideal. If fluid viscosity can be maintained in the optimum range, typically 25 to 36 centistokes, the overall efficiency of the hydraulic system is maximized (less input power is given up to heat). But it is important to remember that multigrade does not automatically mean “one size fits all.” If the system is required to operate in freezing temperatures in winter and tropical conditions in summer, multigrade will do a better job of maintaining viscosity within permissible limits across a wide range of temperatures. Is multigrade hydraulic oil always better?Įnvironment and equipment type are two main considerations for choosing a multigrade type of hydraulic oil. Once you understand the basics yourself, you can ask better questions of a potential supplier or oil as a service partner to identify your lubricant needs and choose the right grade, additive, or detergent properties for your equipment. While it is not possible to make one definitive recommendation that covers all types of hydraulic equipment in all applications, there are a few key questions to ask yourself when considering different additive packages and other hydraulic fluid options. But often it is the many additive, detergent and other finer points of choosing a hydraulic oil that leads to confusion or misunderstandings. Hydraulic oil can range from full synthetic (to handle drastic temperature and pressure swings) to water-based fluids (used in applications where there is a risk of fire). The chemical makeup of a hydraulic fluid is the basis for many other decisions when selecting hydraulic fluid for your equipment. Heat transfer, power transfer, and lubrication are all critical aspects of hydraulic fluid performance. Hydraulic fluid plays many different roles in the operation of a hydraulic equipment, whether mobile or stationary.
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