How can the flow rate of a tank be controlled using only the difference in liquid levels? !
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A large tank that discharges water outward based solely on the liquid level; at the beginning, with a high liquid level, the flow rate is certainly high. Now, valve control is added to regulate flow. How does valve control ensure a constant flow rate? Is it necessary to add PLC control to gradually adjust the valve opening? Is there any simpler way? Please give me some advice!
By adding an overflow port, the water won’t flow to other places
Make a hole at the bottom of the tank, insert a pipe, bend it upward, and set its height at the highest liquid level. The principle is that when the water level reaches the inlet of the overflow pipe, it can be discharged. With a larger pipe diameter, it is basically not restricted by flow rate. The pipes outside the tank can be disposed of freely at any level below the highest water level.
As the liquid level keeps dropping and the driving force keeps decreasing, how can the flow rate remain constant? !
It would be best to send a flowchart for easier discussion. If your requirement is for a stable supply flow rate from the tank outward, it is necessary to control the driving force of the fluid, thereby maintaining a constant output volume based on changes in the pressure before the valve. It is advisable to install a pneumatic control valve; if the flow rate required is low and the pressure before the valve is high, a self-acting control valve can also be considered for regulation. For reference.
All three elements are required: a flow meter, a PLC (either a simple PLC or some other control unit), and control valves equipped with positioners. Control via springs or other self-acting mechanisms does not seem to work
The flow rate in a pipe is determined by two factors: 1. The pressure difference between the two ends of the pipe； 2. Pipeline resistance. When the pipe resistance remains constant (with the valve opening unchanged), the flow rate changes as the pressure difference across the pipe changes (due to variations in the liquid level before the valve); it cannot remain constant. To maintain a constant flow rate when the pressure difference changes, it is necessary to alter the pipe resistance; in other words, the valve opening must be changed.