A hydraulic fluid has the following four primary functions:
1. Transmit power
2. Lubricate moving parts
3. Seal clearances between mating parts
4. Dissipate heat
In addition a hydraulic fluid must be inexpensive and readily available.To accomplish properly the four primary functions and be practical from a safety and cost point of view, a hydraulic fluid should have the following properties:
1. Good lubricity
2. Ideal viscosity
3. Chemical stability
4. Compatibility with system materials
5. High degree of in compressibility
6. Fire resistance
7. Good heat-transfer capability
8. Low density
9. Foam resistance
10. Nontoxicity
11. Low volatility