Flow control valve, in the measurement of heating systems, occupy a very important position. Therefore, how to correctly select the flow control valve and design, it is particularly crucial! This article starts with the structure and working principle of the flow control valve, and puts forward the problems that should be paid attention to in the selection and design of the control valve. Thermostatic valve in the selection of the design, with the selection of the same diameter pipe temperature control valve, but also to the selected temperature control valve to create an ideal working conditions of pressure; electric control valve is suitable for computer monitoring System for flow control equipment, generally more unattended in the thermal station to use; For manual balance method, how to use the valve characteristic curve analysis of the valve regulating performance, how to solve the valve in the case of small opening valve easy Leading to the phenomenon of the impact of steam hit; self-flow control valve in the design and selection of the valve to note the minimum work poor requirements. Keywords: Temperature control valve Electric control valve Balance valve Differential pressure control valve Heating system The implementation of heat metering charges can save energy and improve energy efficiency of the heating system. As far as the current situation is concerned, the energy efficiency of our heating system is only about 30%. People often only pay attention to the boiler and the heat loss of the network, while ignoring the heat user heat loss. Thermal user heat loss, mainly due to uneven heat caused by this part of the heat loss of about 30 ~ 40%, is quite impressive. Heat metering system to engage in charging, from the energy point of view, mainly to tap this part of the potential for energy saving. Metering charges mainly through three ways of macro-energy: First, the installation of the flow control valve, to achieve the flow balance, thereby overcoming the uneven heating and cooling; followed by the role of temperature control valve, the use of solar energy, appliances, lighting, etc. Equipment, free heat; the third is to raise the awareness of energy saving with residents, reducing unnecessary windows and other heat. The three energy-saving ways, of which two are through the flow control valve to achieve. Can be seen, flow control valve, heating system in the measurement of charges, what occupies an important position. Therefore, how to correctly select the design of flow control valve, it is very important. First, the temperature control valve 1, the radiator thermostatic valve structure and working principle The user's indoor temperature control is achieved through the radiator thermostatic control valve. Radiator thermostatic control valve is a thermostat controller, flow control valve and a pair of connectors, of which the thermostat is the core component of the sensor unit, that temperature package. Temperature package can sense changes in the ambient temperature and volume changes, drive the valve spool displacement, and then adjust the radiator water to change the radiator heat dissipation. Thermostatic valve set temperature can be artificially adjusted, thermostatic valve will be set according to the requirements of automatic control and adjust the radiator water, in order to achieve the purpose of controlling the indoor temperature. Temperature control valve is generally installed in front of the radiator, through the automatic regulation of flow, to achieve the residents need room temperature. There are two thermostatic valve thermostatic valve and thermostatic valve three points. The three-way thermostatic valve is mainly used for single-pipe system with crossing pipe. The shunt coefficient can vary from 0% to 100%, and the flow control has a large space but the price is more expensive. The structure is complicated. Two-way thermostatic valve for some double-tube system, and some for single-tube system. The two-way thermostatic valve used in the two-pipe system has greater resistance; the one-pipe system used has less resistance. Thermostatic valve temperature sensor package and the valve body is generally assembled into a whole, the temperature package itself is the scene of the indoor temperature sensor. If desired, a remote temperature sensor can be used; the remote temperature sensor is placed in a room requiring temperature control and the valve body is placed in a location on the heating system. 2, the design of temperature control valve temperature control valve is the heating system flow control of the most important regulation equipment, and other control valves are auxiliary equipment, temperature control valve is essential. A heating system without the thermostatic valve can not be called the so-called heat metering and charging system. In the design of temperature control valve, the correct selection is very important. The purpose of temperature control valve selection, according to the design flow (known heat load), allowing the resistance to determine KV value (flow coefficient); then KV value to determine the temperature control valve diameter (model). Therefore, the design catalog or manufacturer's samples must give the relationship between KV value and diameter, otherwise it is not convenient for designers to use. Selection of temperature control valve design, by no means simply select the same diameter with the pipeline temperature control valve that is down. But in the selection process, the selected temperature control valve to create an ideal working conditions of pressure. A temperature control valve usually working pressure difference between 2 ~ 3mH2O, the maximum does not exceed 6 ~ 10mH2O. To this end, we must give the temperature control valve preset range of values ​​to prevent noise, affecting the normal operation of temperature control valve. When the same KV value, there are more than two choices of caliber, should be given priority to choose a small caliber thermostatic valve, the purpose is to improve the thermostatic valve regulating performance. Second, the electric control valve Electric control valve is suitable for computer monitoring system to adjust the flow of equipment. Mostly used in unattended thermal stations. Electric control valve by the valve body, drive mechanism and transmitter components. Thermostatic valve is self-flow through the temperature control package flow regulation equipment, does not require external power supply; and electric control valve generally require single-phase 220V power supply, usually as a computer monitoring system actuator (regulating flow). Electric control valve or thermostatic valve are the most important equipment in the heating system flow regulation, the rest are its ancillary equipment. Third, balance valve Balance valve points manual balance valve and self-balancing valve. Both manual balancing valve or self-balancing valve, their role is to increase the proximal end of the heating system to increase resistance, limiting the actual operating flow should not exceed the design flow; in other words, its role is to overcome the redundant heating system proximal With ram, the electric control valve or thermostatic valve can work under a permitted pressure head. Therefore, the manual balancing valve and self-balancing valve, they are all thermostatic valve or electric control valve auxiliary flow regulator, but it is very important, if the selection is not properly designed or unreasonable, electric control valve or temperature control Valves do not work well. 1, manual balancing valve 1.1 Manual balancing valve works Manual balancing valve is a one-time manual adjustment, can not automatically change with the system operating conditions change resistance coefficient, so called static balance valve. The object of manual balancing valve is resistance, can play the role of manually adjustable orifice to balance the resistance of the pipe network system, to achieve the balance of resistance of each loop role. Can solve the system steady-state imbalance problem: when the operating conditions are different from the design conditions, the circulating water is more or less than the design conditions, the balance valve is balanced by the system resistance, the new water volume can be designed according to the proportion of balance The flow of each branch will be increased or decreased in proportion at the same time and still meet the flow requirements corresponding to the current load 1.2 Problems to be noticed in the design and selection of manual balancing valve (2) (1) The characteristic curve of the valve is decided The valve regulating performance, such as the closing valve flow curve, if 95% ~ 100% of the traffic flow that is meaningless, then the opening from 0 to 5% of the flow that is achieved throughout the change, so the valve is It can not be used as a balance of water conservancy conditions. As the theoretical curve of the valve is measured under the top pressure difference, and the actual conditions as long as the valve authority is not 1, the valve in the small opening line valve before and after the pressure difference, the opening is the valve before and after the pressure difference, resulting in valve dG / dC value in the small opening becomes larger, smaller opening in the large opening, so that the actual work of the valve to open the direction of the deviation, the smaller the valve power the greater the deviation, the linear characteristics of the valve due to the actual performance Offset will lead to effective adjustment of the valve opening degree of space becomes smaller, so the theoretical curve of the valve string below the arc as a percentage of the characteristics as well. Equal percentage curve valve, the valve authority of 0.3 ~ 0.5 actual working curve may be close to the linear characteristics. (2) Normally, the flow rate of the valve is too high when the valve is small, and the turbulent swirling zone will be formed after the valve. The vortex zone and the new pressure are very low, where the pressure is lower than the saturated pressure corresponding to the water temperature The flash of water vapor leads to the phenomenon of steam blow: severe noise, vibration of valves and pipes, damage of valves, pipes and pipe supports. Prevention and control of such accidents First of all, in the design of the valve runner to consider the valve seat and valve seat in the small opening to form a narrow throttle passage, constrained the formation of strong turbulent vortex; followed by the valve to maximize the valve Degrees, to avoid the valve in the small opening of the operation. In addition, as far as possible without pressure conditions involved in the problem of alkaline balance valve installed in the water back to the lower water pipes. 2, self-balancing valve 2.1 self-balancing valve works Self-balancing valve can be in the absence of external power supply, the system automatically balances traffic. Self-balancing valve is to maintain the orifice (fixed aperture) before and after the differential pressure to achieve a limited flow, therefore, can also be called the flow valve. Fixed flow valve is the role of object flow, to lock the flow of water through the valve, rather than against the balance of resistance. He can solve the system's dynamic imbalance: In order to maintain the efficient operation of a single chiller, boiler, cooling tower, heat exchanger these devices need to control the flow of these devices is fixed at the rated value; From the end of the system, in order to avoid Dynamic adjustment of the interaction, but also need to end the flow of devices or branches. The problem should be noted in the design Self-flow flow control valve has the drawback of the valve is the minimum work poor requirements, the general requirements of the product minimum working pressure 20KPa, if installed in the most adverse circuit, will inevitably require more circulating water pump 2 m water column The work lift, it should be taken near-end installation, distal uneasy method. Do not install this self-operated flow control valve when the user is at a distance greater than 80% of the heating radius from the heat source. Fourth, the differential pressure control valve 1, the principle of differential pressure control valve Differential pressure control valve principle, in essence, and self-balancing valve is the same. However, self-balancing valve, the orifice plate is present as a component in the valve body; and differential pressure control valve without the orifice of this component, but the system behind the differential pressure regulator valve as a plate, Therefore, the differential pressure control valve actually refers to the system after the entrance pressure difference. As can be seen from the structure of the differential pressure regulating valve: This control valve, the purpose is to control the subsequent system pressure difference between the entrance and exit fixed. The basic function is based on the thermal user demand for heat load, automatically adjust the thermal user's operating flow. When a building due to some hot users require room temperature decreases, the corresponding room temperature control valve opening becomes smaller, resulting in differential pressure control valve pressure value becomes larger than the set value, then the differential pressure control valve automatically Off small spool, increase throttling effect, to reduce the pressure drop of the system, until the return to set value. The ultimate effect is to reduce the flow, to meet the needs of hot users, in order to reduce the frequent operation of the temperature control valve. When the heat user requests to raise the room temperature, the function of the differential pressure regulating valve is the opposite (3). 2, the design should pay attention to the problem Some people think that in the indoor system or standpipe, should be installed pressure control valve. After the simulation calculation: If the building's hot inlet, the uniform installation of a balanced valve (including manual, self-operated) or pressure regulating valve (but the design should be reasonable), the indoor temperature control valve in any adjustment range, before and after the pressure Poor will not exceed 6 ~ 10mH2O, temperature control valve can work under reasonable conditions. Therefore, it is not necessary and expensive to install a differential pressure control valve excessively. Fifth, the circulating pump variable flow operation, the choice of flow control valve Here mainly refers to the manual balancing valve, self-balancing valve and pressure regulating valve selection. In the circulating pump variable flow operation, the manual balance valve showed a geometric imbalance, the most conducive to the operation of temperature control valve; but the disadvantage is manual operation too much, it is difficult to achieve the desired adjustment. Circulating pump variable flow operation, the hot user entry the ideal setting pressure value should be with the outdoor temperature changes. For this, self-balancing valve, differential pressure regulating valve, are not ideal, but will not appear out of control. Therefore, this type of control valve can be used, which is beneficial to improve the regulation performance of the heating system.
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