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Selection method of hydraulic oil viscosity

Release Date: May 18, 2017
Selection of hydraulic oil viscosity
After selecting the right type, it is also necessary to determine what viscosity grade of hydraulic oil is used to make the hydraulic system work at its best. If the viscosity is too high, it is good for lubricity, but it increases the resistance of the system, the pressure loss increases, the power loss increases, the oil temperature rises, the hydraulic operation is unstable, and noise occurs. Excessive viscosity can also cause difficulty in absorbing oil during low-temperature startup, and even interrupt oil supply during low-temperature startup, resulting in equipment failure. On the contrary, when the viscosity of the hydraulic system is too low, it will increase the internal and external leakage of the hydraulic equipment, the operating pressure of the hydraulic system is unstable, the pressure is reduced, the hydraulic working parts are not in place, and the pump wear will increase in severe cases.
The choice of viscosity level depends on the type of pump. Each type of pump has its optimal viscosity range: 25 ~ 68mm2 / S for vane pumps and 30 ~ 115mm2 / S for plunger and gear pumps. The minimum working viscosity of the vane pump should not be less than 10mm2 / S, and the maximum starting viscosity should not be greater than 700mm2 / S. The minimum working viscosity of the plunger pump should not be lower than 8mm2 / S, and the maximum starting viscosity should not be greater than 1000mm2 / S. Gear pumps require large viscosity, the minimum working viscosity should not be lower than 20mm2 / S, and the maximum starting viscosity can reach 2000mm2 / S.
When selecting the viscosity level, the working conditions of the pump must also be considered. For hydraulic systems with high temperature and pressure, hydraulic oil with higher viscosity must be used to obtain better lubricity. On the contrary, lower temperature and pressure should be used. This saves energy. In addition, it should also be considered that the operating viscosity of the hydraulic oil at the lowest temperature of the system should not be greater than the maximum viscosity of the pump. Table 3 lists the viscosity choices for various pumps at different pressures and temperatures.