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Types and working principles of common flow control valves

There are three main ways to save energy through metering and charging: first, a flow regulating valve is installed to achieve flow balance, thereby overcoming the phenomenon of uneven heating and cooling; second, through the function of a temperature control valve, the use of solar energy, home appliances, lighting, etc. The free heat of equipment; the third is to improve the energy-saving awareness of heat-consuming residents, and reduce unnecessary heat dissipation such as opening windows. And of these three energy-saving ways, two of them are realized by flow control valve. It can be seen that the flow regulating valve occupies an important position in the heating system of metering and charging. Therefore, how to correctly carry out the selection and design of the flow control valve is very important.

1. Electric control valve
Electric regulating valve is a device suitable for flow regulation in computer monitoring system. Generally used in unattended thermal stations. Electric regulating valve consists of valve body, driving mechanism and transmitter. The temperature control valve is a device for self-operated flow regulation through the temperature sensor package, and does not require an external power supply; while the electric control valve generally requires a single-phase 220V power supply, which is usually used as the actuator of the computer monitoring system (regulating the flow). Electric regulating valve or temperature control valve is the most important equipment for flow regulation in heating system, and others are auxiliary equipment.

2. Balance valve
The balance valve is divided into manual balance valve and self-operated balance valve. No matter the manual balance valve or the self-operated balance valve, their function is to increase the resistance at the proximal end of the heating system and limit the actual operating flow to not exceed the design flow; in other words, its function is to overcome the excess resources at the proximal end of the heating system. Use the pressure head to make the electric regulating valve or temperature control valve work under a permitted capital pressure head. Therefore, manual balancing valves and self-acting balancing valves are auxiliary flow adjustment devices for temperature control valves or electric control valves, but they are very important. Valves don't work very well.

2.1. Manual balance valve
2.1.1. Working principle of manual balance valve

The manual balance valve is manually adjusted at one time and cannot automatically change the resistance coefficient with the change of the system operating conditions, so it is called a static balance valve. The object of the manual balance valve is resistance, which can play the role of a manually adjustable orifice plate to balance the resistance of the pipe network system and achieve the role of resistance balance of each loop. It can solve the problem of steady state imbalance of the system: when the operating conditions are different from the design conditions, the circulating water volume is more or less than the design conditions. Since the balance valve balances the system resistance, the new water volume can be balanced according to the proportion of the design calculation. distribution, so that the flow of each branch will increase or decrease proportionally at the same time, and still meet the corresponding flow requirements under the current load

2.1.2. Problems that should be paid attention to in the selection and design of manual balance valve

(1) The valve characteristic curve determines the adjustment performance of the valve, such as the flow curve of the globe valve. If it is considered that the flow change between 95% and 100% is meaningless, then the opening degree from 0 to 5% can realize the flow rate. The whole process changes, such a valve cannot be used as a balance adjustment for water conservancy conditions. Since the theoretical characteristic curve of the valve is measured under the top pressure difference, and the actual working condition as long as the valve authority is not 1, the valve will have a large pressure difference before and after the valve at the small opening line, and the large opening will be a small pressure difference before and after the valve, resulting in the valve dG The value of /dC becomes larger at a small opening, and becomes smaller at a large opening, so that the actual working curve of the valve shifts to the direction of quick opening. The smaller the valve authority, the greater the shift. The offset will lead to a smaller opening space for the effective adjustment of the valve, so the theoretical curve of the valve is better to have a sub-chord arc such as an equal percentage characteristic. For the valve with equal percentage characteristic curve, the actual working curve may be close to the linear characteristic when the valve authority is 0.3 to 0.5.

(2) Usually the flow rate of the valve is too high when the valve opening is small, and a strong turbulent vortex area will be formed after the valve. The vortex area and the new pressure are very low. The flashing of water vapor leads to the phenomenon of water hammer: severe noise, vibration of valves and pipes, damage to valves, pipes, and pipe supports. To prevent this kind of accident, first consider the valve plug and valve seat to form a narrow and long throttling channel when the valve opening is small, and restrict the formation of strong turbulent vortex in the design of the valve flow channel; secondly, try to increase the valve power when selecting the valve. degrees to avoid valve operation at small openings. In addition, when the problem of pressure conditions is not involved, try to install the alkali balance valve on the return pipe with a lower water temperature.

2.2. Self-operated balancing valve
The self-operated balancing valve can automatically realize the flow balance of the system without external power supply. The self-operated balancing valve realizes the flow limitation by maintaining a constant pressure difference between the front and rear of the orifice plate (fixed aperture). Therefore, it can also be called a constant flow valve.

The object of the constant flow valve is the flow, which can lock the amount of water flowing through the valve, rather than the balance of resistance. He can solve the problem of dynamic imbalance of the system: in order to maintain the high-efficiency operation of a single refrigerator, boiler, cooling tower, and heat exchanger, it is necessary to control the flow of these devices to be fixed at the rated value; from the end of the system, in order to avoid The interplay of dynamic regulation also requires flow restriction at the end device or branch.

In the design, it should be noted that the disadvantage of the self-operated flow control valve is that the valve has a minimum working difference requirement. Generally, the minimum working pressure difference is 20KPa. If it is installed on the most unfavorable circuit, it is bound to require an additional 2 meters of water column for the circulating pump. The working head should be installed at the near end, and the far end should be uneasy. Do not install this self-operated flow control valve when the distance between the user and the heat source is greater than 80% of the heating radius.

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