tailieunhanh - HYDRAULIC SYSTEMS

One of the results of the study of fluid mechanics has been the development of the use of hydraulic oil, a so-called incompressible fluid, for performing useful work. Fluids have been used to transmit power for many centuries, the most available fluid being water. While water is cheap and usually readily available, it does | CHAPTER 60 HYDRAULIC SYSTEMS Hugh R. Martin University of Waterloo Waterloo Ontario Canada HYDRAULIC FLUIDS 1831 SYSTEM CLASSIFICATIONS 1847 CONTAMINATION CONTROL 1832 PUMP SETS AND ACCUMULATORS 1847 POSITIVE ASPECTS OF CONTAMINATION 1833 HYDROSTATIC TRANSMISSIONS 1851 DESIGN EQUATIONS-ORIFICES AND VALVES 1834 CONCEPT OF FEEDBACK CONTROL IN HYDRAULICS 1852 DESIGN EQUATIONS PIPES AND FITTINGS 1835 IMPROVED MODEL 1854 HYDROSTATIC PUMPS AND ELECTROHYDRAULIC MOTORS 1838 SYSTEMS ANALOG 1856 STIFFNESS IN HYDRAULIC ELECTROHYDRAULIC SYSTEMS 1843 SYSTEMS DIGITAL 1860 HYDRAULIC FLUIDS One of the results of the study of fluid mechanics has been the development of the use of hydraulic oil a so-called incompressible fluid for performing useful work. Fluids have been used to transmit power for many centuries the most available fluid being water. While water is cheap and usually readily available it does have the distinct disadvantages of promoting rusting of freezing to a solid and of having relatively poor lubrication properties. Mineral oils have provided superior properties. Much of the success of modem hydraulic oils is due to the relative ease with which their properties can be altered by the use of additives such as rust and foam inhibitors without significantly changing fluid characteristics. Although hydraulic oil is used mainly to transmit fluid power it must also 1 provide lubrication for moving parts such as spool valves 2 absorb and transfer heat generated within the system and 3 remain stable both in storage and in use over a wide range of possible physical and chemical changes. It is estimated that 75 of all hydraulic equipment problems are directly related to the improper use of oil in the system. Contamination control in the system is a very important aspect of circuit design. In certain industries such as mining and nuclear power it is critically important to control the potential .