Viscosity is another major factor for choosing a hydraulic fluid. All the advantageous or exclusive properties of a hydraulic oil are useless if the viscosity grade of the oil is not in-sync with the operating temperature of the given system. Inappropriate viscosity can lead to underutilization of the potential component life. There are a number of factors involved in setting the appropriate fluid viscosity grade for a given hydraulic system, such as:
-The initial viscosity at the lowest ambient temperature
-Utmost anticipated operating temperature which is actually determined by the maximum ambient temperature.
-Proper and permissible viscosity range as per the system's components.
Though making a choice regarding the suitable hydraulic oil is a little difficult, hence, here are few tips which can help you make a definitive choice for the same that too according to your hydraulic system and application.
Multigrade / Monograde Oil
Now, in case the hydraulic system is needed to operate in low temperature or tropical conditions then it is advised to use multigrade oil in order to maintain the viscosity within allowed limits spanning across a varied range of operating temperature. If the viscosity of the given fluid can be appropriately maintained, i.e. around 25 to 36 centistrokes, the hydraulic system would become more efficient by using lesser input power to heat up. This indicates that multigrade fluid helps a great deal in reducing the electricity consumption of a given hydraulic system. It is a lot more advantageous for mobile hydraulic equipment users as it helps in reducing the fuel consumption. Though an expert would never advise to use multigrade oil in case a system has lesser range of operating temperature and somehow it is possible to maintain fluid viscosity by using a monograde oil.
Detergent Oil
Detergent oils are best known for emulsifying water and dispelling and arresting other contaminants like sludge or varnish. Generally, DIN 51524; HLP-D fluids, also known as antiwear hydraulic fluids, are the ones that comprised of detergents and dispersants. Most of the hydraulic component manufacturer endorse the use of these oils for contaminant free components. But the contaminants in case of detergent oils need to be filtered out since they do not settle out. Detergent oils are well suited for mobile hydraulic systems as they are relatively smaller in size and hence, have less chances of contaminants deposition and precipitation. Water is extremely dangerous for any hydraulic system as it alone can lead to multiple problems like corrosion, oil aging, reduced lubricity etc. The advantage of using detergent oils is that emulsified water can easily be turned into steam at highly loaded parts of the system and detergent oils help in emulsifying the water content.
Anti wear Oil
Anti wear oils are basically used to maintain lubrication within the permissible limits. Now-a-days the most commonly used antiwear additive in engine and hydraulic oil is Zinc Dialkyl Dithiophosphate, alternatively, ZDDP. Though the use or presence of ZDDP is not always recommended as it is notorious for assaulting the metals by either chemically breaking them down or reducing their fiterability. Today, the advanced and stabilized ZDDP chemistry has essentially managed to overcome these problems, thus, transforming it into an important additive for all the high performance hydraulic systems. In fact, it renders advantageous for the mobile applications too with a combine concentration of about 900 parts per million.
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