Will too low an outlet flow velocity of the pump reduce the head?
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Due to process requirements, pumps with a head of 50 m each and flow rates of 50, 400, and 720 m3/h are connected in parallel. The manifold is selected to handle a flow rate of 1200 m3/h at a flow velocity of 3 m/s. When only the pump with a flow rate of 50 m3/h is in operation, the flow velocity in the manifold is below 0.2 m/s; under such conditions, can a head of 50 m be achieved?
My personal opinion: The flow rate at the pipe junction has decreased, but the flow rate at the pump outlet remains unchanged; therefore, the flow volume also remains unchanged. Thus, based on the head-flow curve, it can be concluded that the head remains the same, at 50 meters.
The head will not be low, but the pressure drop needs to be checked
In my understanding, with the pump and piping remaining unchanged, the larger the pipe diameter, the lower the flow velocity; both the frictional losses along the pipeline and the local losses decrease as a result. Therefore, more head capacity should be available in practical use. But I’ve seen many sources state that the outlet flow velocity falls within a certain range, such as 1–3 m/s; I’m not sure whether there will be any adverse effects if the velocity is below this range. I would appreciate some guidance from those who know more.
The head does not change; it depends only on the pump itself and has nothing to do with the pipes
As long as the water can fill the system, the head remains constant. This is similar to the effect of air pressure… If there is any change, it’s that the head will increase slightly, because when the pipes are larger, the pressure loss in the pipes is reduced, and consequently the pump’s head becomes higher. This experiment is easy to conduct; just think about a U-tube manometer to understand the principle. However, it’s important to ensure that the pump’s inlet is enlarged accordingly, otherwise the outflow speed may not be sufficient, resulting in the larger pipes at the outlet not being filled completely… and thus the desired head cannot be achieved.
The head will not change; it has little to do with the inlet flow velocity
The head will drop; it’s likely that you can’t even open your outlet valve fully, otherwise the pump will shut down
There are two scenarios to consider. In the case of a head of 1.50 meters, it is mainly used to overcome the height difference over which the fluid needs to be transported; in such a situation, the pump’s head should remain unchanged and can reach 50 meters； A head of 2.50 meters is mainly used to overcome the horizontal transfer distance, and this situation may lead to the problem mentioned above. This is because the actual operating point of the pump is the intersection of the pump’s own operating curve and the pipeline characteristic curve. The current situation is that the flow rate has decreased significantly, and the resistance in the pipes has also dropped a lot, leading to overflow.
In practice, the main considerations are the transfer height and the loss due to local resistance; the horizontal transfer distance can be ignored (it’s no more than 20 meters). According to the person upstairs, the head pressure should remain unchanged. Furthermore, in actual use, the outlet pipeline and the high-level water tank are always filled with water. When the pump stops, the outlet valve is closed; when it starts operating, the water pump is turned on first for about 1 minute before the valve is opened. Will this ensure normal operation?
The head of the pump has nothing to do with the condition at the pump’s outlet. . . The pipeline is smaller than the pump outlet; the pump’s head remains unchanged, only the flow resistance inside the pipe increases, resulting in a lower actual outlet pressure. . . The pipeline is larger than the pump’s outlet; the pump’s head remains unchanged, but the fluid in the pipeline may become stagnant. For a small pump with a capacity of 50 cubic meters, using a pipeline that is over 1 meter in diameter to convey water means that the pipeline may not even be filled completely if it is placed horizontally. . . :lol
It should still be 50 feet of head. This is mainly related to the pump’s flow rate and power; if the power remains unchanged and the flow rate does not exceed the pump’s normal level, then the head will not decrease – in fact, it might even increase
This situation should work.
Flow rate and head should have nothing to do with each other, right?