The use of hydraulic oil for excavators

1. Select hydraulic oil reasonably

① Viscosity of hydraulic oil

The principle for determining the viscosity of hydraulic oil is to keep the viscosity of the hydraulic oil (used for components such as pumps and motors) within the optimal range (16-36 × 10-6mm ² /s), taking into account the working temperature and efficiency of the hydraulic circuit. The viscosity of the short-term cold start corresponding to the lowest ambient temperature is ≤1000 × 10-6mm ² /s. And the viscosity at the maximum allowable leakage oil temperature of 90℃ for a short period of time is ≥10 × 10 ⁻ ⁶ mm ² /s.

② Viscosity Index (VI

This indicator directly reflects the property that the viscosity of the oil changes with temperature (i.e., the viscosity-temperature characteristic of the oil). A higher viscosity index of the oil indicates that the degree to which the viscosity of this type of oil changes with temperature is relatively small. Conversely, it is larger. The viscosity index of anti-wear hydraulic oil from well-known foreign manufacturers (such as Mobil, Shell, etc.) is VI≥110, while that of domestic high-grade anti-wear hydraulic oil is around 95. The viscosity index of high-viscosity index hydraulic oil (HV) and multi-grade engine oil produced abroad is all VI>140. This point requires special attention from users who use large imported hydraulic excavators and adopt domestic hydraulic oil (or use engine oil as hydraulic oil). A decrease in viscosity index will narrow the range of environmental temperatures that the oil can adapt to. If it is absolutely necessary to use it, relevant information should be consulted with the oil manufacturer. The application range of the oil should be appropriately adjusted, and if necessary, the relevant setting values of the equipment (such as the limit temperature, etc.) should also be changed.

③ Other comprehensive performances

Due to the high working pressure of the hydraulic system of modern large hydraulic excavators (≥32MPa), the maximum allowable working oil temperature of the hydraulic oil is also relatively high (around 90℃). Therefore, in order to ensure the normal operation of the hydraulic system within the normal oil change cycle, It is required that the oil selected for the system has excellent qualities in terms of lubricity, oxidation stability, anti-wear, rust and corrosion prevention, anti-emulsification, anti-foaming, shear stability and extreme pressure load resistance.

2. A good hydraulic oil cooling system

For the improvement of the hydraulic oil cooling system (more precisely, the hydraulic oil temperature control system) of large hydraulic excavators, although the specific methods adopted by different manufacturers may vary, the basic idea is the same: to keep the hydraulic oil temperature balanced within a relatively ideal range during continuous operation. It can also enable the hydraulic system to heat up rapidly when it is put into operation in a cold state (reaching the normal working temperature range of the oil). Under the condition of using qualified hydraulic oil, when the hydraulic oil overheats, the inspection steps for the hydraulic oil heat dissipation and temperature control system are as follows:

Check if there is any dirt blocking the hydraulic oil radiator, which may cause a decrease in heat dissipation efficiency. Clean the radiator if necessary.

② Under extreme conditions, detect the actual working pressure of the fan speed system to determine whether there are faults in the hydraulic components of this circuit and whether the oil temperature sensor or control circuit is working properly. At this point, both the fan speed and the system working pressure should be at their maximum values. Otherwise, the corresponding parameters of the system should be adjusted or the damaged components replaced.

3. Inspection of relevant hydraulic parameters in the system

At present, there are mainly two control methods for the working pumps of large hydraulic excavators: ultimate load regulation (GLR) with pressure CUT-OFF function (i.e., cut-off function) and load sensing regulation (LS). The function of the CUT-OFF feature is that when the system working pressure reaches the set value, the swash plate deflection Angle of the variable pump decreases, allowing the pump to only maintain the "residual" flow state required to keep that pressure, thereby preventing the overflow of the relief valve from causing overheating. To achieve this purpose, the system parameters are matched so that the set value of the CUT-OFF valve is lower than that of the primary pressure valve in the circuit as per the technical requirements. Otherwise, opening the primary pressure valve will cause the overflow to overheat.

At the same time, check whether the secondary valve is working properly. This work must be carried out strictly in accordance with the technical requirements. If necessary, restorative adjustments should be made to the relevant system parameters.

4. Eliminate abnormal internal leakage

It mainly refers to abnormal internal leakage caused by the jamming of directional valves and pressure valves due to the contamination of the system's hydraulic oil. The inspection methods: measure the pressure, check the function, or listen for any abnormal noise (the "throttling flushing sound" caused by the valve port not closing tightly), or touch to check if the temperature is locally too high.

5. Prevent the volumetric efficiency of components from declining

Both abnormal wear and normal wear should be taken seriously. The former may occur within a very short period of time and can be judged by checking the quality of the oil and combining it with the functionality of the system (such as whether the actuating elements operate normally and whether the speed has decreased, etc.). The latter should follow certain rules, be comprehensively examined and measures should be taken in a timely manner.