In the building automation system (BAS), the actuator is the last link, it is an indispensable part in the various control systems, and its importance is self-evident. Reasonable choice and the proper use of the actuator will be the realization of smart technology to play an active role. The actuator is the end member of the automatic control system, for example, regulating valves, dampers, and the adjusting means of the electric heater and solenoid valve, wherein the regulating valve is the most widely used in the intelligent building an actuator. In the heating, ventilation and air conditioning systems use a large number of control valves door. Actuators a direct impact on whether the system can work properly.
??Actuator principle is relatively simple in design often people neglect this part. In fact, the actuators in the environment of the production site, long-term and production of media contacts to ensure its safe operation is not an easy task, building automation system, it is also the weak link. Since the design of the actuator maintained improper or run poorly, often the whole automatic control system is not normal, or seriously affect the regulation of quality and lead to failure of the entire system. Intelligent Building Systems has completed a considerable part of the control system is unsatisfactory, although not all the problems caused by the actuator, but it does account for a considerable proportion. Floor word automation system must give redouble attention to the selection and application of the actuator, should pay attention to the selection of the actuator, from the design stage to carefully consider the requirements of the application until the installation details, pay attention to consider a variety of factors, including human factors, advanced nature of the objective evaluation of the program. Cost should strive to achieve leading technology, reasonable price, so be configured to meet the requirements. Doing can truly seamless connectivity components and systems. Optimized engineering design is an important guarantee to achieve the intended purpose and effect.
??Choice of control valve door
??Floor word system of heating, ventilation and air conditioning systems, often using various control valves doors, such as chilled water, hot water control. Selection control valve gate valve caliber selection, model selection, the flow characteristics of the valve selection and valve material selection, including housing, spool seat. The same time, the degree of protection of the valve, control signals, power supply, rated power, leakage, also need to consider the maximum differential pressure and ambient temperature.
??Adjust the valve door caliber choice
??Process parameters adjusts the flow capacity of the valve, in order to determine the caliber size. Suppose excellent control characteristics, the regulator valve caliber choice has become the key to controlling the quality of good or bad. Some designers empirically estimated the the valve aperture size, not to be carefully calculated and checked, it is sometimes difficult to select enough reasonable. In another case, is to do the HVAC engineer this part of the work is completely entrusted to the control engineer to do, it will also have some problems, choose the regulator valve is usually considered more control over quality control engineers, may lead to the caliber small. In fact, by HVAC engineers choose to adjust the valves better, because they are more familiar with the charged object and pipeline characteristics. Adjust the flow capacity of the valve, the control must take into account the quality of the design, the parties to the communication, coordination. Commonly used in most engineering principle is to select a small-caliber valve as much as possible under the conditions to meet the flow capacity.
??Adjust the diameter of the valve gate is determined according to the flow capacity of the process requirements. The flow capacity regulating valve door directly reflect the capacity of the regulating valve, it is designed, the choice of the main parameters regulating valve. Regulating the flow valve and the spool, the structure of the valve seat, the valve differential pressure, fluid properties and other factors. The flow capacity of the calculation is to determine the most important theoretical basis of the regulating valve diameter, but its calculation methods at home and abroad has not yet unified. Our country under the flow capacity is defined as: when the valve is fully open, the valve pressure at both ends of 0.1Mpa, the fluid density number 100kS/m3 per hour flowing through the flow regulating valve (m3 / h) C. Engineering calculations are determined by calculating the flow capacity regulating valve size, some valve manufacturer in the user manual selector valve diameter calculation tables. Medium flows through the regulating valve in the HVAC system is mainly water, steam, The formula C values ??can be checked in the Design Manual.
??Regulate the flow characteristics of the valve gate options
??Appropriateness of the flow characteristics of the valve valve work is good or bad, is directly related to the to select spool flow characteristics should be based on the characteristics of the process object. Regulating valve flow characteristics mean that the medium flows through the relationship between the relative degree of opening of the valve relative flow with the valve is adjusted. Depending on the shape of the spool, divided into linear, equal percentage and quick opening three. Under normal circumstances, the regulating valve and so the percentage flow characteristic can adapt to the load variation occasions, Guchang priority selection.
??For adjusting the characteristics of the object, considering the mating of the valve flow characteristics with the object, the feature is extremely important for the improvement of the entire system. The object load changes, piping and adjust the quality of the case should be considered. For example, the control of the hot water heater or pipe resistance is larger when a substantial change in system load, should elect the percentage flow characteristic. If the control is certain differential pressure or a steam heater or a valve before the load change is small, the linear flow characteristics should be selected.
??Body Structure Model choice
??In addition to the valve diameter need to be calculated and determined according to the application, the choice of the regulating valve structure models is also very important. Many occasions, due to the valve structure models the improper control system can not operate properly or failed to run. To this end, according to the process conditions and fluid properties, considering a reasonable choice to adjust the valve structure. Floor word automation system regulation valve: through single seat valve, straight through the seat valves and three-way valve. In addition, due to the excellent performance of the sleeve valve, eccentric rotary valve, ball valves and butterfly valves, its application is increasingly widespread.
??Through single seat valve
??The main features are: through single seat valve equipoise, a small amount of leakage, easy off, allowable pressure, flow capacity. This valve is suitable for applications requiring a small amount of leakage and less pressure occasions (when a large pressure difference must be selected thrust implementing agencies or equipped with a valve locator).
??Through engine valve
??The main features are: through engine valves unbalanced force is small, large leakage allowable pressure, flow capacity, suitable for occasions strict with leakage and differential pressure. Through engine valve due to the complexity of the flow path of the valve body, it does not apply to the high viscosity and fiber-containing medium occasions.
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