Common hydraulic fluids

Hydraulic fittings are used to seal the hydraulic oil or fluid within the system. Thus, the fittings should be compatible with the fluid being used. Hydraulic fluid provides the energy to the system allowing the machinery to perform its work. There are different types of hydraulic media in the market.

• Petroleum-based fluids: Petroleum or mineral-based fluid is the most used hydraulic fluid. Additives in such fluids provide protection from rust and oxidation, wear and tear, corrosion, and extreme pressure. These fluids are generally high quality, low cost, and widely available.

• Water-based fluids: These fluids have high water content, so, they are used for fire-resistance. They are available as water-in-oil emulsions, oil-in-water emulsions, and water-glycol blends. They are more expensive than petroleum-based fluids and have lower wear resistance.

• Synthetic-based fluids: These fluids are man-made and provide advantages like fire-resistance, lower friction, and thermal stability. They are ideal to use in high-temperature and high-pressure applications due to their excellent lubricating property. However, they are more expensive than petroleum-based fluids and maybe slightly toxic.

Selection criteria & points of attention

The following criteria should be considered before selecting the correct hydraulic fitting types for your application:

1. Size: The internal and external diameter of the fittings are two important sizes to consider. These diameters of the fitting should be compatible with the hose diameter. Over or under-sized fittings can cause leakage or the connection to fail.

2. Material: The material of the hydraulic fitting should be compatible with the hydraulic fluid and with the operating environment. The most commonly used fitting materials are brass, aluminum, steel, or stainless steel. NBR (Nitrile) O-rings are the most widely used sealing materials.

3. Temperature: The hydraulic fittings should be suitable for your temperature range.

4. Pressure: The hydraulic fittings must be suitable for your pressure range, including the pressure spikes. Operating beyond this range can cause damage to the fittings.

5. Application: The type of application also determines the fitting type to be used. Tee- or cross- fittings are used for mixing or distribution application.

6. Assembly: If the hydraulic system requires frequent connecting and disconnecting of the hose or tube, the hydraulic quick-connect fittings can be used. Similarly, hydraulic compression fittings can be used to remove the need for welding or soldering of the fitting. It uses a compression nut to tighten against the ferrule creating a very tight seal. It can be used in areas with high temperatures as welded joints can leak in such environments.