Pressure before and after the control valve
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As the title suggests, in the parameters table of the control valve, the pressure before the valve is 0.8 MPa and the pressure after the valve is 0.5 MPa. What does this mean? Does it mean that when the pressure before the valve is 0.8 MPa, the pressure after the valve remains at 0.5 MPa regardless of the opening degree of the control valve?
There are many parameters that affect the calculation process of control valves. It can be seen from the formula. I suggest you address it from a fundamental perspective: look at the textbooks, then use the examples in them to work through the calculations on your own and you’ll understand it.
To understand a problem, one should not take things out of context; if what is connected to your throttle valve is at atmospheric pressure, would these issues still occur? It should be connected to the pipeline of the device, and it is the pressure within the connected pipeline equipment that constitutes the pressure behind the valve (on a macro scale).
The pressures before and after the valve listed in the control valve parameter table refer to the pressures that should exist before and after the valve under normal operational conditions.
For example, if there is a pump in front of the valve, check the pump’s head; if there is equipment behind the valve, check the resistance of that equipment. That’s roughly what it means.
4# is right. Specifically, under ideal stable operating conditions, the control valve is set at a certain opening degree, resulting in a pressure of 0.5 behind the valve. When fluctuations occur, the opening degree of the control valve changes in order to mitigate these disturbances, and as a result the pressure behind the valve is no longer 0.5. It returns to 0.5 after the interference is eliminated.
No, when the valve is closed, the pressure behind it definitely decreases. The pressure behind the valve refers to the pressure at a certain opening degree of the valve under normal flow conditions
It might be due to the usage requirements for the pipeline. The normal pressure before the valve is 8 kilograms, while the required operating pressure after the valve is 5 kilograms. In other words, the control valve needs to adjust the pressure so as to maintain a pressure of 5 kilograms behind the valve
I agree with you; control valves come with information on the pressure before and after the valve, and it is based on this pressure that the appropriate control valve is selected!