The correct selection and application of regulator

At present in the field of automatic control, whether a process can satisfy the process control indicators, the control process is smooth, overshoot amount, damping ratio, whether the disturbance within the prescribed scope, is stable, fast, accurate, in addition to the process design is reasonable, the equipment is advanced, the important thing is that the regulator can according to the main body consciousness and accurate operation, which controls the process of the main body consciousness embodied in the material energy and flow change accurately. In many automatic control, because the regulator quality closes nevertheless, poor flow characteristic, large leakage, action is unreliable and make the automatic control lost high quality regulation, brought great economic losses to the production, and increase the intensity of labor. Because the regulator in the process piping installation, direct contact with the operating medium, long-term under high temperature, high pressure, corrosion and friction, etc. The influence of the bad working conditions. So, the quality of the regulating valve selection control function relationship between the system. Therefore, the correct reasonable choice, install the regulator is important. The selection of regulating valve 1. 1 valve type selection is mainly based on the characteristics of the media, control requirements, installation environment factors such as combining the flow characteristic and the structure of the regulator itself to choose, as shown in table 1. Should also be considered when choosing the regulator on the cover and used in the form of packing. When using the working temperature for - 20 ℃ ~ + 250 ℃ when, need to adopt the structure of the ordinary; When the temperature of the work for - When 50 ℃ ~ + 450 ℃, should adopt the bonnet with multi-layer heat sink cooling structure. And bellows corrugated chamber sealing cover is mainly used for highly toxic, volatile, easy penetration, and other important medium. Regulator commonly used packing with ptfe and asbestos rope packing, although the former expensive but the sealing effect is much better than the latter. Gas, gas close type valve selection should be based on when air pressure signal interruption, regulating valve open or closed position to process on the size of the damage. If the valve is in open position when the harmfulness of small choose gas type. Action process is: the angry is closed, no gas is open; If the valve is in closed position when the harmfulness of small, choose open gas, action process is: the wind is open, no gas is closed. 1. 2 regulator caliber choice in automation technology renovation, such as valve diameter can be based on the principle of sectional area, according to the manual operation when the valve diameter, and open circle count how many estimated open area, and then choose open under normal conditions with the same area of the regulator. In the design of the new device is usually according to the flow capacity C value to determine the diameter of the valve. There are two commonly used methods. (1) according to the actual maximum flow Qmax Cmax calculate the corresponding circulation ability, and then pick up slightly from the product line is greater than the Cmax C values and the corresponding valve diameter, when choose, should leave room for necessary, finally, the actual maximum calculating the flow valve opening of Qmax: when Qmax opening should be no greater than 90%. (2) the more practical way is according to the common flow to calculate the corresponding the flow capacity of Cvc. Choose the valve C value should make Cvc/C in 0. 25 ~ 0. Between 8, according to the commonly used traffic Cvc value multiplied by ( 4 to 1. 25) , in general, Cvc/C = 0. 5 to the right. When work for logarithmic characteristic can be smaller. , 1. The choice of 3 valve flow characteristics, Instrument and meter plant) 1. 3. 1 from the control system regulation quality analysis considering principles: appropriate selection characteristic of regulating valve, valve amplification coefficient changes to compensate the regulator the changes to the amplification coefficient, make the overall adjustment system amplification coefficient remains constant control effect. 1. 3. 2 analysis at the scene of the production, the process piping valve together with total and pipeline equipment, inevitably there is resistance, regulating valve work flow characteristic is different from ideal flow characteristic. Therefore, first should be according to the characteristics of the control system characteristic of regulating valve in table 2 process piping note: S valve fully open the differential pressure and differential pressure of the system total value. Choose hope to get the job characteristics, and then consider the process piping is to select the corresponding ideal characteristics. Table 2 for reference. 1. 3. 3 changes from load analysis in a small open of the straight line valve when the flow rate change is big, adjust too sensitive, easy to cause oscillation, thus unfavorable use in S small load change is big occasions; Percentage valve such as amplification coefficient increases with increasing the valve stroke, flow relative change is constant, so it is suitable for the occasion, big load changes in quick opening characteristics of general used for on-off valve regulation and process control applications. The installation of two regulator ( Kaidi instrument equipment factory) Regulating valve in use reasonable installation, will ensure his good control effect in the control system. The installation of the regulating valve, general should pay attention to the following points. (1) the regulator shall be installed in horizontal pipe runs vertically, if you must tilt or horizontal installation should be added support. Before and after the valve should have more than 10 times the diameter of straight pipe length. (2) the flow of fluid should be like the signs on the valve body. (3) the installation site should be easy to repair, and is equipped with bypass. (4) when the valve diameter smaller than the pipe size, should connect the taper tube ( General to make valve control effect is obvious, pipe size is greater than the calibre of the valve. ) (5) in the case of low ambient temperature, regulator should add with heat pipe.