An interesting question regarding pipeline pressure
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It is a horizontal straight pipe with water as the fluid, flowing from left to right; a differential pressure flow meter is used to measure the flow rate. The balance valve in the three-valve assembly is open, resulting in a differential pressure of 0. The problem is that water flows due to a pressure difference; now that the pressure difference is 0, how can we explain the phenomenon of water flow? (It has nothing to do with the throttling device – we are looking at the pipeline in the three-valve assembly.) Suppose the pressure tapping tubes are located at the beginning and end of the pipeline; then, will opening the balance valve result in a differential pressure value? (It should.) There is no need for guessing now; what’s needed are scientific formulas for calculating the differential pressure. Another issue is: how to determine the differential pressure when the pipeline is vertical or inclined.
Under normal circumstances, when the balance valve is open, the differential pressure should be 0; it has nothing to do with water flow. If the pipes are vertical or inclined, even when the water is at rest, the reading on the gauge will include the pressure due to the height of the liquid column inside the pipes. When the balance valve is opened, the gauge reading returns to 0
There is actually a pressure difference; it’s just that the two points you selected are too close to each other
1. A differential pressure flow meter measures the pressure difference before and after a throttling element, under the action of that throttling element； 2. The reason for water flowing in pipes is not solely due to the pressure difference between the front and back; this is not the primary factor. The primary factors are the continuous energy supply provided by the pump and the supply of water itself ； 3. When the balance valve is opened, the differential pressure flow meter can only indicate “I can’t do it.” The pressure difference that was painstakingly created by the throttling element is then released by the balance valve. Do you think a balance valve is there for fun?
For fluids, pressure is divided into static pressure and dynamic pressure. What is static pressure? What is dynamic pressure? How to measure static pressure and dynamic pressure? What is the relationship between dynamic pressure, static pressure, and flow velocity? Can flow velocity and flow rate be measured without installing throttling devices on the pipeline? Classical fluid dynamics theory has covered these issues in great detail; there’s really nothing \"interesting\" about them. :Lol, the original poster should go and check out that textbook. .
It’s not that there is no differential pressure, but the differential pressure is too small to detect. After the balance valve is opened, the pressure acting on the differential transducer is the pressure drop that occurs at both ends of the balance valve, as the pressure difference across the throttling element drives the flow of the fluid in the pressure guiding tube. The method of opening the balance valve to bring the differential back to zero can only be used as a reference. After the balance valve is opened, there are numerous factors that can prevent the difference from returning to zero……