Ascending Efficiency: Rising Stem Valves in Critical Process Control
Nov 21,2023Read More
The control valve does not need any external energy, and relies on the pressure change of the medium to be adjusted for automatic adjustment, eliminating the residual pressure head of the pipe network and the flow change caused by pressure fluctuations. It can keep the pressure difference between users' inlet and outlet constant, especially suitable for household metering or automatic control system, which is helpful for the stability of the system during operation.
The working characteristic curve of the control valve is different when the pressure difference of the pipe network outside is different. Therefore, when designing and selecting the pipe network, it should be ensured that the pressure difference of the pipe network at the installation position of the valve changes within the allowable range of the valve. The actual pressure difference that is too large or too small will cause the spring to fail, resulting in the valve not working properly.
The set pressure difference of the control valve should match the resistance of the pipeline system in the valve under the design flow rate to ensure that the valve works in its optimal working area. If the difference between the two is too large, the actual flow of the pipeline system in the valve will be too large, which will cause the hydraulic imbalance of the pipeline system outside or cause the actual flow of the pipeline system in the valve to be too small, which will affect the heating effect.
Control valves of different diameters control different flow ranges. When selecting a valve, the design flow of the piping system in the valve should be taken within the optimal working area of the valve control flow range according to the working characteristic curve of the valve. If the valve diameter is too small, it will make the valve work at the high end of its control flow range, and it is easy to generate noise. If the valve diameter is too large, the valve will work at the low end of its control flow range, and the system flow change range is too large, which will easily cause hydraulic imbalance in the piping system outside, and will also cause economic waste. Generally, the diameter of the valve is equal to or one size smaller than that of the pipe system interface in the valve.
The purpose of the control valve is for the user to adjust the flow according to the heat demand within a certain range. The heating system using the control valve is a variable system. However, at present, most of the heating pipe networks are determined according to the basic needs of heating, and it is difficult for the pipe network system to supply unrestricted heating on demand, which will inevitably cause the hydraulic imbalance of the pipe network system. The hydraulic imbalance is particularly serious, especially in the heating system where only the control valve is installed but the heat meter is not installed. In the current transitional stage from meeting basic heating needs to on-demand heating, there are two solutions:
1. Increase the flow of the pipe network;
2. Limit the flow at the thermal inlet or on the branch lines.
The method to restrict the flow is to set the flow control valve. The flow control valve can choose a self-operated flow control valve, so that the pipe network can automatically balance the flow. A self-operated flow control valve is installed at each thermal inlet, which is more expensive and therefore less used. Another way is to set up a self-operated flow control valve on the branch line. At present, the vast majority of thermal inlets use locking flow control valves, which requires manual mediation at the initial stage of operation of the pipeline network, which is time-consuming, labor-intensive, complicated, and difficult to adapt to the change of working conditions of the thermal network. But this is an economical measure to ensure the hydraulic balance of the heating network.
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