For any hydraulic system to run efficiently and safely it is vital that you use the correct hydraulic fluid.The primary function of the fluid is to transfer power from the pump to the rest of your hydraulic system. Furthermore, hydraulic fluid lubricates parts, prevents wear and tear, and acts as a heat transfer medium.

What are the different fluid types?

Hydraulic fluids can be categorized into three main types, synthetic-based, mineral-based, or water-based. Each type having its own set of characteristics that must be carefully considered when choosing the right fluid for your system.

Synthetic fluid - This is a manmade lubricant and works well in high-pressure, high-temperature systems. Some may contain phosphate esters for fire resistance.

Petroleum-based / mineral-based fluids – These are the most widely used in industry today. They often contain extra additives such as rust and corrosion inhibitors, extreme pressure agents, anti-wear properties, and even colourful dyes that can help identify leaks.

Water-based fluids – These fluids are useful in applications where there could be a potential fire hazard. Water-based fluids have high water content and when a system gets very hot the water in the emulsion turns to vapour and helps to cool the system down.

Viscosity Index

Viscosity is how a hydraulic fluid's resistance to flow is measured. Fluid will resist compression at different rates. Hydraulic fluids will have an ISO grade assigned to them, ISO stands for the International Standards Organisation. The higher the VG number the thicker the fluid. Some of the most common types are

ISO VG 32 - ideal for use in high-powered machine tools.

ISO VG 46 - ideal for industrial machinery working under high pressure.

ISO VG 68 - ideal for large load-carrying hydraulic systems.

Uses of Hydraulic Fluid

Aircraft use hydraulics to allow pilots to operate the mechanical flight controls due to the effort it would take them normally. It is also stored in the accumulators for self-starting the aircraft's main engines.

Other equipment that uses hydraulic fluids are excavators, power transmission and power steering systems, refuse trucks, lifts, and hydraulic brakes.