When using hydraulic oils, understanding the viscosity of the oil you require for your machine is vital to prevent damage and maximise function efficiency. The viscosity of the oil conducts the oil’s resistance and ability to flow. A highly viscous oil will be thicker and slower moving, more difficult to compress, whereas an oil with a lower viscosity will be much thinner, able to flow more easily.
We measure the viscosity of hydraulic oil in units of Centistokes (cSt) using a viscometer, at temperatures either of 40 or 100 degrees centigrade. This temperature is essential to determining the viscosity as without this the cSt is useless.
This measurement is graded as ISO VG, set by the International Standards Organisation - the higher the VG, the higher the viscosity. There may also be a W alongside this rating which represents the oil’s weight unlike with automobile oils which refer to winter oil.
You can see an example of how this might be written below and where each type of oil may be used.
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ISO 15 Hydraulic Oil – ISO VG 15 Hydraulic Fluid is typically used in power steering and hydraulic brake systems.
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ISO 22 Hydraulic Oil – ISO VG 22 Hydraulic Fluid is generally used in airlines for air tools etc.
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ISO 32 Hydraulic Oil – ISO VG 32 Hydraulic Fluid is ideal for use in high-powered machine tools.
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ISO 46 Hydraulic Oil – ISO VG 46 Hydraulic Fluid is normally required for industrial plant working under high-pressure etc.
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ISO 68 Hydraulic Oil – ISO VG 68 Hydraulic Fluid is designed for use in systems which require a large load-carrying ability.
So there you have it! Hopefully you can now be safe in the knowledge that you can purchase the most suitable oil at the perfect viscosity for your machine.
