Hydraulic Oil
The terms hydraulic oil and hydraulic fluid are at times used interchangeably, although they do similar jobs they are quite different products and cannot safely be interchanged in most applications. They are both fluids, but hydraulic fluid is made up of a number of different fluids. This can include pure, fresh water, water-oil emulsions and salt solutions. An important difference is that hydraulic fluid, unlike hydraulic oil is not flammable, a major disadvantage, which is why it’s used in situations where flammability is an issue such as in vehicles, aircraft electrical and marine applications. Multi grade oils with viscosity index improvers were starting to be used eighty years ago in high performance vehicles and for other high speed applications. Now this common and very well tested technology is being used to make most of the standard high viscosity index oils used in today’s automotive transmission fluids as well as gear oils. Unfortunately, these viscosity improvers do not usually have the right share stable characteristic of hydraulic oil and so are mostly not suitable for heavy, modern, high pressure, hydraulic systems. Hydraulic oils with its inherent bulk modulus properties can have its viscosity index improved by using high base stocked synthetics and polymers to meet the high demands of industrial hydraulics. Properties of Hydraulic Oil For hydraulic oil to be effective it needs a range of properties that other lubricants share as well as special qualities that make it unique, such as:
- Foaming resitance as well as good air release characteristics
- To be stable at high temperatures
- Have a low oxidation rate
- To be hydrolytically stable
- High anti-wear performance
- Be easily filtered
- Demulsibility
- Have a good anti-rusting and corrosion inhibiting properties
- Able to maintain viscosity regarding film thickness
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