Pressure difference issue before and after the water replenishment control valve in the water seal tank

The pressure behind the valve is taken as the actual pressure, while the maximum pressure drop is based on the maximum pressure before the valve; this determines the output force of the actuator!

I’ve been confused as to whether the pressure after the valve refers to the pressure at the end of the pipeline behind the valve (the water seal tank), or the pressure right after the control valve

If the flow is discharged directly into the air behind the control valve, then the pressure behind the valve will be zero. However, some valve manufacturers claim that when the pressure behind the valve is zero, no water flow occurs. According to this view, the pressure behind the valve should be the pressure desired; the higher this pressure, the greater the flow rate

First of all, I’m not an expert in this field; could you send a flowchart? Guessingly, the source of signal for the actuator of a control valve should be the point that needs to be controlled; factors such as pressure, temperature, and liquid level behind the valve, as well as those in front of the valve, are all suitable control points. It is presumed that using a liquid level as a reference point for atmospheric pressure conditions is much more accurate than using a pressure point Just a guess, for reference.

“How should the pressure behind the valve be determined? ” No pictures, no truth; I can’t figure out what the connection is between water sealing and the pressure behind the valve, so I’m trying to find out. How is it connected when the tube is turned off? By installing a small pressure regulator, the level of pressure becomes clear and obvious, making it very easy to \"determine\" it accurately....... :lol

The original poster might be overcomplicating things. The pressure behind the valve can be considered to be at atmospheric pressure; once the valve is opened, the 5 kilograms of pressure ahead will push the medium toward the back of the valve. So why worry about the pressure behind the valve being zero?

Many process engineers are confused about how to determine the pressure conditions before and after a control valve. Simply put, the pressures required for a control valve are calculated based on the pressure drop across the valve at its maximum or normal opening degree; these are not the actual pressure values before and after the valve in the pipeline. Taking the questioner’s issue as an example, wouldn’t the pressure downstream be at atmospheric pressure if this control valve isn’t installed? The conclusion is clear: the 5 MPa pressure drop cannot be entirely attributed to the valve; rather, it is caused by the equipment in the pipeline downstream. Therefore, the pressure before and after the valve cannot be increased to 5 MPa. As for what the appropriate pressure drop should be, there is the concept of valve resistance ratio, which refers to the proportion of the pressure drop across the valve to the total pressure drop in the pipeline.