Problems with the flow rate of high-speed centrifugal pumps
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Our factory uses high-speed centrifugal pumps to transport gasoline, but it seems that their flow rate isn’t very high – it’s even lower than that of ordinary centrifugal pumps. Sometimes, when the liquid level is high, we have to use two pumps to transfer the gasoline. I’m not sure why this is the case Moreover, the outlet valve of the pump cannot be opened too wide, otherwise the outlet pressure will drop. Why is this the case?
1. Is the flow rate of your pump insufficient because a too-small pump was selected? High-speed pumps are generally used to increase head, not to increase flow rate. To increase flow rate, it is much more economical to use a larger conventional centrifugal pump rather than a high-speed pump. 2. The flow rate and head of a water pump are inversely proportional; as the flow rate increases, the head decreases and the operating current rises ； As the flow rate decreases, the head increases and the operating current decreases. Pumps have performance curve charts, as well as efficiency curve charts, with their optimal operating efficiency points. In a situation like the one you described, when the valve is opened wider, the outlet pressure decreases, and that is because the flow rate is too high. It is unsafe and uneconomical for a water pump to operate under such conditions for long periods, as it results in excessive current consumption and low efficiency.
Reply to 2# zhiyuan1100: Is it necessary to fully open the outlet valve of the high-speed centrifugal pump? When we use a pump to draw water, an overcurrent occurs when the outlet valve is opened wide; however, when transporting gasoline, no overcurrent occurs even with the outlet valve open wide, but the flow rate does not increase.
Reply to 3# Cuihua Yisu: Water has a higher density than gasoline; therefore, for the same volume pumped, the flow rate is different
Both high-speed pumps and centrifugal pumps have characteristic curves, and they can operate properly only within a certain flow rate range. High-speed pumps are generally characterized by a very high head but a low flow rate (if a high flow rate is required, multi-stage centrifugal pumps would be more suitable). So the original poster thinks it’s normal for the high-speed pump to have a low flow rate. However, be sure not to open the valve too wide; if it is opened too much, the pressure drop will be excessive, which can easily damage the pump.
It seems that the pump you selected is not suitable for the current operating conditions; a larger high-speed pump or a multi-stage pump would be more appropriate for the current situation
The outlet valve of the high-speed pump in our unit is fully open. The maximum flow requirement for our process is 60 T/H, so a pump with a capacity of 70 T/H was selected. The excess amount is returned, so there has been no issue with low pressure.
Reply to 3# Cuihua Yisu: It’s true that the outlet valve of the high-speed pump doesn’t need to be fully open, but it shouldn’t prevent pressure from rising either, right? However, the outlet valve cannot be opened too much, as this will cause pump congestion and an increase in temperature.
Check whether the pump’s inlet filter is clogged, or if there is air in the pump’s inlet and outlet. The pump design should be fine.
Reply to 8# zhiyuan1100: Not bad; it’s common to experience situations where the pump cannot deliver sufficient flow and the temperature of the pump’s inlet pipeline is high. We sometimes water the inlet pipeline with fresh water.
Reply to 9# gz7513: The filter is fine; it’s clean inside when opened. There should also be no gas presence.