Seeking help regarding the pump’s head and flow rate
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This post was last edited by jiahongleiqw on 2019-10-23 at 19:39. With the same piping system, a pump from one manufacturer is capable of meeting the required flow rate and head pressure; however, when another manufacturer’s pump is used, the flow rate increases significantly while the head pressure decreases greatly. It becomes necessary to close the pump outlet valve to half its opening in order to achieve the desired pressure and flow rate, but the pressure required at the user end downstream of the outlet valve cannot be guaranteed. What is the reason?
The pumps from the two manufacturers have the same rated flow rate and rated head
The flow rate of the other pump is low; check whether the inlet filter is clogged
The pump outlet valve must be closed to half in order to achieve the required pressure and flow rate, but the user pressure required after the outlet valve cannot be guaranteed. Are these two sentences contradictory? ? ? ? ?
1. Based on the information provided, both pumps are capable of meeting the pressure and flow requirements at their operating points. 2. Since they are products from different manufacturers, their hydraulic characteristics may not be identical; it’s also possible that the manufacturers used different settings for the rated points and operating points, resulting in different performance curves. 3. The operating point of a pump during operation is the intersection of the pump’s performance curve and the pipeline’s performance curve. Because the performance curves of the two pumps differ, it is necessary to adjust the pipeline characteristics in order to achieve the same requirements. In the case of the second pump, reducing the outlet valve opening is a way of adjusting the pipeline characteristics to meet the required conditions. 4. The poster mentioned that reducing the outlet valve opening could affect the pressure requirements of users downstream; this raises the question of whether the backpressure in the pipeline is also altered 4.1. When transporting liquid media, due to the incompressible nature of these media, as long as the flow rate remains constant, the resistance loss in the pipeline downstream of the pump outlet valve is constant; closing the outlet valve creates a local resistance. 4.2. If the pipeline is very long, the proportion of this local resistance caused by the outlet valve becomes small, to the point where it can be ignored. 4.3. Additionally, if the back pressure in the pipeline is high, the pressure at the user’s end will also be high; conversely, if the back pressure is low, the pressure at the user’s end will be low, and this too affects the proportion of local resistance caused by the valve. 5. In general, the local resistance of a single valve is not sufficient to have a significant impact overall; if such an impact does occur, it indicates that the pipelines at the user’s end have very little elasticity and are quite fragile.
The answer upstairs is quite comprehensive. It is likely that the performance curves of the two pumps are different; although their rated operating points are the same, the trends in flow rate and head for the two pumps vary when they deviate from those rated conditions. It seems that the flow rate and head curves for the second pump are more gradual. As for solutions, there aren’t any good suggestions either; if possible, try replacing the impeller of the second pump with one that has a narrower flow channel.
The parameters specified for the pump are different from those used in operation, resulting in differences in the performance curve.
Products from different manufacturers vary in size, structure, and thus their performance curves also differ
View the pump’s performance curve, calculate pipeline fluid dynamics, and determine the appropriate match for the pump