There are monogrades and multigrade hydraulic oils, but the most important variable in selecting a hydraulic fluid is viscosity and specifically, maintaining viscosity over the entire operating temperature range of the equipment, says Jeff Snyder, industrial brand specialist for Chevron Lubricants. The key factors needed to select the right fluid include pump and equipment specification, the load put on the fluid or component, pump type, operating conditions and applications. Each OEM specifies the type of hydraulic fluid and viscosity grade suitable for their machines, says Alex Smith, heavy-duty off-road, natural gas segment manager for Castrol. Unlike engine oils, there is no universal spec for hydraulic oil. They must be changed every 250 to 500 hours, they bear the brunt of all the heat, soot and a pressure cooker environment inside today’s emission compliant engines.īut hydraulic fluids are also important and deserve your attention even if you only change them every 2,000 hours or more. Engine oil on the right emulsifies the water making it less efficient as a hydraulic fluid.Įngine lubricating oils get a lot of attention in heavy equipment maintenance schedules and for good reason.
The HF should be tested on seal & elastomer compatibility.Hydraulic fluid at left clearly separates out, or de-emulsifies, the water that accumulates in the system.
Influencing parameters are water, contamination, degraded oil components, air and system design. This is a common problem in hydraulic system. Foaming: after the oil is agitated and aerated, it generates a foam.Air causes poor system efficiency and cavitation. Air release: the ability of the oil to release enclosed air.The rate of oxidation is influenced by high temperature, water and wear metals (catalysts). Thermal and oxidation stability: chemical reaction of O 2 with oil form acidic byproducts.Viscosity Index (VI): value that indicates the effect of temperature on the viscosity high VI fluids maintain their viscosity relatively well with temperature changes.Zn based additives are considers as the most common, while Zn-free additives are recommended for environmental reasons or in case of corrosion or hydrolysis problems. There are two types: Zn based (zinc diakyl dithio phosphate ZDDP) and Zn-free based.
Anti-wear properties: anti-wear additives form a thin reactive layer on the surface to prevent direct metal-to-metal contact.Next to the viscosity, a hydraulic fluid has several other parameters that influence system performance: The fluid viscosity determines both the mechanical efficiency and the volumetric efficiency and sets the limits of the optimum operating range of a hydraulic system. Choosing a hydraulic fluid with the right viscosity is primordial for the overall efficiency of the hydraulic system. High temperatures result in lower viscosity and vice versa. The HF viscosity is influenced by ambient and operating temperature and system design. Other negative effects of a high fluid viscosity are cavitation, poor air release and inadequate lubrication. This generates energy losses and unnecessary heat generation. If the fluid viscosity is too high, the system will suffer from a sluggish movement and a reduced mechanical efficiency. Low viscosity fluids also increase the risk of internal leakages generating a lower volumetric efficiency of pumps and motors. If the hydraulic fluid viscosity is too low, the oil film will be too thin causing direct metal to metal contact which leads to excessive wear on components.