Problems with the pump shut-off pressure in the pipeline
Thread Content
There is a great confusion regarding a centrifugal pump that is used to pump water to a height of 10 meters. If the valve at the outlet of the equipment is closed, both the equipment and the pipes have to withstand the pressure resulting from the pump being turned off. The question is whether the pressure in the pipe at 10m is the same as the pressure at the pump outlet, which is at 0m Some might say it’s different, because of the difference in static pressure. The results I obtained using Aspen’s dynamic simulation are indeed the same. My doubt is that in this system, it is the pump that continuously provides pressure; therefore, the pressure throughout the entire system should be the same, and it isn’t simply a gravity-based environment. I appreciate your advice. Thank you!
In a horizontal pipe filled with liquid, the pressure should be the same everywhere. For vertical pipes, there is a static pressure difference.
Calculation is one issue; in practice, it might be a different situation. The actual head of the pump in operation may differ from that specified during selection
Head is merely the capacity of a pump; moreover, as LZ mentioned, it cannot be a positive-displacement pump. When calculating pipelines, factors such as pipeline resistance and gravity are taken into account
Does LZ mean that the pump keeps generating pressure, and the pressure will keep increasing over time? No, this force does not accumulate
After the pump is turned off, it no longer supplies energy to the liquid in the pipeline; at this point, the pressure at the pump outlet corresponds to the static pressure of the liquid at a height of 10 meters
I’m not saying that the pressure increases over time; what I mean is that the pump is in a closed-pressure state, and it keeps running to generate pressure. So I think this is not a simple gravity field environment; it’s not as simple as having individual 10-m pipes filled with liquid columns. . .
The pump isn’t turned off; it’s the shutdown head of the pump that comes into play, meaning the pump is running idle with liquid filling it, with the outlet valve closed~~~ If the pump is indeed turned off, then you are correct.
The design requirement for the shut-off pressure of centrifugal pumps is 120% of the rated pressure; at shut-off positions where a head difference exists, the static pressure must be removed. This is also why the equipment pressure is generally taken as the top pressure.
Chapter 1 of Principles of Chemical Engineering: Bernoulli’s Equation
If the pipe outlet is closed, the pump will not maintain pressure continuously; it only keeps the outlet pressure at a certain level. The maximum pressure that a pump can generate is fixed. Theoretically, when the pipe is closed, the pressure at the pump outlet equals the intersection point of the performance curve and the vertical axis