How To Choose Hydraulic Fluid Types

Hydraulic Fluid Types

Hydraulic fluid are available in many different blends or mixtures. The proper type to use for a specific system depends a great deal on the system and the way in which it operates. The surrounding atmosphere also plays a part in the type of fluid selected for an application. The following types of hydraulic fluids are commonly used in industrial hydraulic system:

Petroleum oils

Oil-in-water emulsions

Water-in-oil emulsions

Water-base glycol

Chlorinated hydrocarbons

Phosphate esters

Silicone

Silicate esters

Information about the fluids, their advantages and their characteristics are shown in the hydraulic fluid comparison chart.

Industrial hydraulic systems usually are designed to operate well with one particular type and grade of fluid. Selection of a fluid is usually based on viscosity, viscosity index, lubricity, film strength and corrosion, rust –fire and oxidation-resistance. Because petroleum oils are not fire resistant the substitution of a petroleum oil fluid for a fire-resistant fluid has to be considered very carefully. Substitution of a fire-resistant fluid having reduced lubricity for a petroleum-based fluid must also be considered very carefully

The viscosity characteristics of water-base fluids are quite different from either the petroleum have mo viscosity index – their viscosity varies according to the percentage of water in the fluid. Viscosity indexes for non water-base fluids range from minus values for some of the phosphate esters to indexes over 100 for silicone.

The corrosion-resistance of most hydraulic fluid is excellent. (However water-glycol can attack magnesium, zinc, and cadmium). In addition to their high corrosion factor water-base fluids have low lubricity when compared with petroleum oils. High water-content hydraulic fluids do not perform well in a system and frequently cause maintenance problem in the components.

Non petroleum fire-resistant fluids may soften or remove paint and varnish and attack neoprene and rubber seals. Strainer  and filter recommendation for these fluids are also different. The true complexity of any contemplated change in the type of hydraulic fluid used in any given system can only be established on the basis of a thorough understanding of the system operation. Consideration must be given to the following:

1. What types of fluids are used in identical or similar systems?
2. What has been the performance of the fluid in the system?
3. Does an examination of the equipment establish that it would be compatible with a different fluid?
4. What types of fluids are recommended by your suppliers?
5. What changes in the existing system would have to be made in order to utilize a different recommended fluid?
6. Can the operating condition be improved in other ways so that a change in fluid is not necessary?
7. What advantages will be gained by changing fluid?