【正文】 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。 militaryindustrial control devices used in artillery, ship anti rolling devices, aircraft simulation, aircraft retractable landing gear and rudder control devices and other devi ces. A plete hydraulic system consists of five parts, namely, power ponents, the implementation of co mponents, control ponents, auxiliary ponents and hydraulic oil. The role of dynamic ponents of the original motive fluid into mechanical energy to the pressure that the hydraulic system of pumps, it is to power the entire hydraulic system. The structure of the form of hydra ulic pump gears are generally 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.。 civil water projects with flo od control and dam gate devices, bed lifts installations, bridges and other manipulation of institutions。 the speed of an actuator depends on how much oil is pumped into it per unit of time. It is possible to regulate flow with a variable displacement pump, but in many circuits it is more practical to use a fixed displacement pump and regulate flow with a volume control valve. Flow Control Methods There are three basic methods of applying volume control actuator speeds. They are meterin, meterout and bleedoff. MeterIn Circuit In meterin operation, the flow control valve is placed between the pump and actuator. In this way, it controls the amount of fluid going into the actuator. Pump delivery in excess of the Metered amount I diverted to tank over the relief valve. With the flow control valve installed in the cylinder line as shown, flow is controlled in one direction. A check valve must be included in the flow control or placed in parallel with it for return flow. If it is desired to control directional valve. The method is highly accurate. It is used in applications where the load continually resists movement of the actuator, such as raising a vertical cylinder under load or pushing a load at a controlled speed. 24 MeterOut Circuit Meterout control is used where the load might tend to run away. The flow control is located where it will restrict exhaust flow from the actuator. To regulate speed in both directions, the valve is installed in the tank line from the directional valve. More often control is needed in only one direction and it is placed in the line between the actuator and direction valve. Here too a bypass check valve would be required for a rapid return stroke. BleedOff Circuit In a bleedoff arrangement, the flow control is bleed off the supply line from the pump and determines the actuator speed by metering a portion of the pump delivery to tank. The advantage is that the pump operates at the pressure required by the work, since excess fluid returns to tank through the flow control instead of through the relief valve. Its disadvantag