How to read the split-range control V-shaped curve. .
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This is the staged control of a pressure storage tank. I had a vague understanding of it when I studied it before, but today, after trying to figure it out further, I’m even less clear about it. According to the V-shaped curve, the inflation valve closes and the pressure relief valve reduces its opening, causing the pressure to rise. Will the pressure increase? In practice, the pressure continues to decrease as the valve is closed further, only at a slower rate. If the hand holding the balloon’s opening is relaxed more, air escapes faster; if it’s relaxed less, air escapes more slowly. Since it’s still a process of pressure release, how can the pressure increase?
1. The pressure controller is a reaction mechanism； 2. Assuming the initial condition is stable, the controller output is at 50%; 3. As pressure increases, the controller output decreases and the vent valve opens, note that the inflation valve is closed at this time, causing the pressure to drop ； 4. Assuming the initial condition is stable, the controller output is at 50%; as the pressure decreases, the controller output increases and the inflation valve opens, note that the vent valve is closed at this time ； 5. Pay attention to the dead zone around 50%, as the tank has a certain pressure-bearing capacity, and this is set to prevent frequent valve operations.
I’m talking about manual control, not including the controller
The last edit to this post was made by ssln123 on 2017-8-8 at 10:57. When valve A is closed further, valve B is also closed, so there is no air supply; as a result, as valve A continues to be closed, the pressure drops further until valve A is completely shut off. Even then, the pressure remains below the set value. After some time (as indicated by the dead zone in the diagram), valve B gradually opens to allow air to be supplied. Then, valve B for overpressure gradually closes; after it has been closed for a certain period of time (there is a dead zone shown in the diagram), if overpressure still exists, valve A gradually opens again. And so on, in a cycle.
When valve A is closed further, valve B is also closed, so there is no air supply. As A continues to be closed, the pressure drops further, until A is completely shut off; at that point the pressure remains below the set value, and then valve B gradually opens to allow air to be supplied. Then, valve B for overpressure gradually closes; after it has been closed for a certain period of time (there is a dead zone shown in the diagram), if overpressure still exists, valve A gradually opens again. And so on, in a cycle.
When valve A is closed further, valve B is also closed, so there is no air supply. As A continues to be closed, the pressure drops further, until A is completely shut off; at that point the pressure remains below the set value, and then valve B gradually opens to allow air to be supplied. Then, valve B for overpressure gradually closes; after it has been closed for a certain period of time (there is a dead zone shown in the diagram), if overpressure still exists, valve A gradually opens again. And so on, in a cycle.
That’s how I understand it: why does the pressure increase as the valve position is reduced for curve A?
It seems that your understanding is completely wrong; the horizontal axis in the graph does not represent the pressure in the storage tank, but rather the pneumatic signal pressure of the control valve. Valve A is a air-actuated valve; as the air signal increases, the valve position moves closer to closed.