Hydraulic oil is the hydraulic fluid used in hydraulic systems that harness the energy of fluid pressure, performing functions such as power transmission, wear protection, system lubrication, corrosion inhibition, rust prevention, and cooling. For hydraulic oil, the primary requirement is to meet the viscosity specifications at both operating and start-up temperatures of the hydraulic equipment. Since the viscosity characteristics of lubricating oils directly affect hydraulic actuation, transmission efficiency, and positioning accuracy, the oil must also exhibit favorable viscosity–temperature performance and shear stability to satisfy the diverse demands of different applications.

1. Ensure that hydraulic oil is not used at high temperatures; oil rapidly oxidizes and degrades under high-temperature conditions.

2. The air filter on the hydraulic station shall be a dual-function filter capable of removing both particulates and moisture.

3. Use precision filter elements to filter the hydraulic oil, ensuring that the oil contamination level is maintained at NAS 8 or lower over the long term. The standard filter elements supplied with the equipment generally have insufficient filtration accuracy and cannot guarantee the required cleanliness of the hydraulic oil. This is because the maximum allowable particle size for contamination in a hydraulic power unit is only 5 µm, whereas the filtration rating of the standard built-in filter is often larger than this value. According to industry standards, the contamination level in most hydraulic power units should be controlled at NAS 8 or lower; for equipment equipped with servo mechanisms, the requirement is even stricter—NAS 7 or lower.

4. Centrifugal dewatering/vacuum dewatering (for oil stations with moisture content).

With proper maintenance, oils such as MOBIL and SHELL can typically last up to five years.

5. Conduct oil condition monitoring on a regular basis.

Hydraulic oil has a wide range of applications and is the most widely used type of industrial lubricant. Currently, hydraulic components are evolving toward smaller sizes and higher power outputs, with system pressures steadily increasing—some have already exceeded 50 MPa. Consequently, the conventional L-HL series is being phased out, while the anti-wear L-HM series is seeing broader application.

6. Prevent air from entering the oil

The oil pump suction port shall be reliably sealed; the suction pipe in the oil tank must not be positioned too close to the oil surface; and an air vent valve shall be installed at the highest point of the system to discharge entrained air from the oil.

7. Rational Design of the Fuel Tank

The suction pipe shall be kept at a sufficient distance from the return pipe, and materials such as lead, zinc, and copper that can catalyze oil oxidation shall be avoided. The inside of the oil tank shall be coated with oil-resistant anti-rust paint, and the cooler installed in the tank must be leak-proof.