【正文】 pump, vane pump and piston pump. Implementation of ponents (such as hydraulic cylinders and hydraulic motors) which is the pressure of the liquid can be converted to mechanical energy to drive the load for a straight line reciprocating movement or rotational movement. Control ponents (that is, the various hydraulic valves) in the hydraulic system to control and regulate the pressure of liquid, flow rate and direction. According to the different control functions, hydraulic pressure control valve can be divided into valves, 27 flow control valves and directional control valve. Pressure control valves are divided into benefits flow valve (safety valve), pressure relief valve, sequence valve, pressure relays, etc.。 directional control valve includes a oneway valve , oneway fluid control valve, shuttle valve, valve and so on. Under the control of different ways, can be divided into the hydraulic valve control switch valve, control valve and set the value of the ratio control valve. Auxiliary ponents, including fuel tanks, oil filters, tubing and pipe joints, seals, pressure gauge, oil level, such as oil dollars. Hydraulic oil in the hydraulic system is the work of the energy transfer medium, there are a variety of mineral oil, emulsion oil hydraulic molding Hop categories. The role of the hydraulic system is to help humanity work. Mainly by the implementation of ponents to rotate or pressure into a reciprocating motion. Hydraulic system and hydraulic power control signal is posed of two parts, the signal control of some parts of the hydraulic power used to drive the control valve movement. Part of the hydraulic power means that the circuit diagram used to show the different functions of the interrelationship between ponents. Containing the source of hydraulic pump, hydraulic motor and auxiliary ponents。 operative or hydraulic cylinder with hydraulic motors, according to the actual requirements of their choice. In the analysis and design of the actual task, the general block diagram shows the actual operation of equi pment. Hollow arrow indicates the signal flow, while the solid arrows that energy flow. Basic hydraulic circuit of the action sequence Control ponents (two fourway valve) and the spring to reset for the implementation of ponents (doubleacting hydraulic cylinder), as well as the extending and retracting the relief valve opened and closed . For the implementation of ponents and control ponents, presentations are based on the corresponding circuit diagram symbols, it also introduced ready made circuit diagram symbols. Working principle of the system, you can turn on all circuits to code. If the first implementation of ponents numbered 0, the control ponents associated with the identifier is 1. Out with the implementation of ponents corresponding to the identifier for the even ponents, then retracting and implementation of ponents corresponding to the identifier for the odd ponents. Hydraulic circuit carried out not only to deal with numbers, but also to deal with the actual device ID, in order to detect system failures. DIN ISO12192 standard definition of the number of ponent position, which includes the following four parts: device ID, circuit ID, ponent ID and ponent ID. The entire system if only one device, device number may be omitted. Practice, another way is to code all of the hydraulic system ponents for numbers at this time, ponents and ponent code should be consistent with the list of numbers. This method is particularly applicable to plex hydraulic control 28 system, each control loop are the corresponding number with the system With mechanical transmission, electrical transmission pared to the hydraulic drive has the following advantages: 1, a variety of hydraulic ponents, can easily and flexibly to layout. 2, light weight, small size, small inertia, fast response. 3, to facilitate manipulation of control, enabling a wide range of stepless speed regulation (speed range of 2020:1). 4, to achieve overload protection automatically. 5, the general use of mineral oil as a working medium, the relative motion can be selflubricating surface, long service life。 the use and maintenance requirements for a higher level of technology. In the hydraulic system and its system, the sealing device to prevent leakage of the work of media within and outside the dust and the intrusion of foreign bodies. Seals played the role of ponents, namely seals. Medium will result in leakage of waste, pollution and environmental machinery and even give rise to malfunctioning machinery and equipment for personal accident. Leakage within the hydraulic system will cause a sharp drop in volumetric efficiency, amounting to less than the required pressure, can not even work. Microinvasive system of dust particles, can cause or exacerbate friction hydraulic ponent wear, and further lead to leakage. Therefore, seals and sealing device is an important hydraulic equipment ponents. The reliability of its work and life, is a measure of the hydraulic system an important indicator of good or bad. In addition to the closed space, are the use of seals, so that two adjacent coupling surface of the gap between the need to control the liquid can be sealed following the smallest gap. In the contact seal, pressed into selfsealstyle and selfstyled selftight seal (ie, sealed lips) two. The three hydraulic system diseases 1, as a result of heat transmission medium (hydraulic oil) in the flow velocity in various parts of the existence of different, resulting in the existence of a liquid within the internal friction of liquids and pipelines at the sam e time there is friction 29 between the inner wall, which are a result of hydraulic the reasons for the oil tempera ture. Temperature will lead to i