Hydraulic Fluid And Temperature Recommendations For Mobile Hydraulic Systems

The oil in a hydraulic system serves as the power transmission medium. It is also the system’s lubricant and coolant. The selection of proper oil is a requirement for satisfactory system performance and life.

In most cases, use of these recommendations will lead to selection of a suitable oil. However, due to the complex nature of oil formulation, the variety of oils available and peculiarities of individual hydraulic applications, there will be rare instances where an oil selected on the basis of these recommendations may yield unsatisfactory results. Vickers cannot be responsible for such exceptions. In this respect, the customer is encouraged to consult his Vickers representative or a reputable oil company when selecting an oil.

Important Factors In Selecting An Oil
Additives
Hydraulic fluids contain a number of additive agents which materially improve various characteristics of oil for hydraulic systems. These additives are selected to reduce wear, increase chemical stability, inhibit corrosion and depress the pour point.

Antiwear
Pump performance and reliability are directly affected by the antiwear additive formulation contained in the oil. Oils providing a high level of antiwear protection are recommended for optimum performance and long life.

Viscosity
Viscosity is the measure of the fluid’s resistance to flow. The oil selected must have proper viscosity to maintain an adequate lubricating film at system operating temperature.

In addition to dynamic lubricating properties, oil must have sufficient body to provide an adequate sealing effect between working parts of pumps, valves,clylinders and motors, but not enough to cause pump cavitation or sluggish valve action. Optimum operating viscosity of the oil should be between 16 cSt (80 SUS) and 40 cSt (180 SUS).

“Viscosity Index” reflects the way viscosity changes with temperature. The smaller the viscosity change, the higher the viscosity index. The viscosity index of hydraulic system oil should not be less than 90. Multiple viscosity oils, such as SAE 10W-30, incorporate additives to improve viscosity index (polymer thickened). These oils should have a minimum viscosity index of 120. Oils of this type generally exhibit both a temporary and permanent decrease in viscosity due to oil shear encountered in the operating hydraulic system. The actual viscosity can, therefore, be far less in the operating hydraulic system than what is shown in normal oil data. Accordingly, when such oils are selected, it is necessary to use those with high shear stability to insure that viscosity remains within recommended limits while in service.

Chemical Stability
Oxidation and thermal stability are essential characteristics of oils for mobile hydraulic systems. The combination of base stocks and additives should be stable during the expected lifetime of the oil when exposed to the environment of these systems.

Suitable Types Of Oil
Crankcase Oil
Oil having an API letter designation SE, SF, SG or SH per SAE J183. Note that one oil may meet one or more of these designations.

Antiwear Hydraulic Oil
These oils are produced by all major oil suppliers and should consist of good quality base stocks compounded with antiwear, antioxidation, antifoam and antirust additives. These may be petroleum, vegetable or synthetic base oil.

Due to the large number of different antiwear hydraulic oils, it is impossible for Vickers to test its products with all of the available fluids. Because of this, an evaluation procedure was developed for fluid suppliers to establish the suitability of their products for use in Vickers components. Refer to “Pump Test Procedure For Evaluation Of Antiwear Hydraulic Fluids For Mobile Systems”, for details of the 35VQ25 test procedure. It is the responsibility of your oil supplier to assure that their fluids meet Vickers requirements.

Environmental Hydraulic Oil
If you have equipment that operates in environmentally sensitive areas, you may consider use of more envionmentally aware fluids. These fluids perform well in our hydraulic systems but may require extra caution in order not to exceed their performance capabilities. For further clarification, refer to Vickers Guide to Alternative Fluids, Bulletin 579.

Other Oils
Certain other types of petroleum oil are suitable if they meet the following provisions:

1. Contain the type and content of antiwear additives found in the above designated crankcase and antiwear hydraulic oils, and have passed the pump tests.

2. Have sufficient chemical stability for mobile hydraulic system service.

3. Meet the viscosity requirements in the Oil Viscosity Recommendations tables.