Does variable frequency control of a pump regulate flow rate but not pressure?

With variable-frequency operation of centrifugal pumps, pressure and flow rate both change. In volumetric pumps, the flow rate varies with speed, while the pressure is determined by the back pressure; if the back pressure remains constant, then the pump’s outlet pressure also remains constant. Therefore, variable-frequency constant-pressure control is applicable to volumetric pumps

The vast majority of people are unclear about these concepts and only know their literal meanings! The vast majority of variable-frequency pumps use pressure sensors to adjust the frequency! ! ! When the rotational speed changes, both flow rate and pressure change, with the pressure change being more significant. The reason and purpose for installing an inverter is that the pump at this station does not operate continuously at its rated capacity; the flow rate we need changes frequently, and the range of these variations is quite large. ”The pressure needs to meet our requirements; it certainly isn’t a fixed value – as long as it satisfies our usage needs, that’s sufficient. This approach helps save energy and protects the pump, and this is what makes a variable-frequency pump useful. At constant pressure, a pressure stabilizing tank is usually installed to maintain the pressure in the water supply system within a certain range. If the pressure drops, a pressure sensor adjusts the pump speed, causing the pump to operate in order to compensate! Not a single value in the entire system remains constant!

Reply to 3#: Both Klaus magnetic pumps and variable-frequency pumps use pressure sensors to adjust the frequency – does this mean that variable-frequency pumps require an inverter and a pressure controller?

It’s not a pressure controller; it’s just a pressure sensor

Reply to 1# Liu Suifeng: I said I know. The reason why a pump uses variable frequency control is to achieve a certain pressure; therefore, variable frequency control in pumps is used to regulate pressure rather than flow rate. This is determined by the pump’s performance curve. When the frequency remains constant, the flow rate can vary significantly, while the change in pressure is relatively small. As shown in the performance curve of a cryogenic pump below

Variable frequency means changing the pump’s speed, thereby altering its performance curve in order to regulate flow rate and head; this is more energy-efficient than changing the characteristics of the pipeline

We all use variable-frequency drives for centrifugal pumps, so both flow rate and pressure can be adjusted

Variable-frequency constant voltage can be achieved

After frequency conversion, an impeller pump can change its flow rate, pressure, and shaft power; the relationship between these parameters is linear, quadratic, or cubic

Frequency conversion involves changing the frequency of the voltage, which in turn changes the speed of the motor; as a result, the speed of the pump also changes. The pump’s speed decreases, and its performance curve shifts toward the origin; at this point, if the system’s curve remains unchanged, both the pump’s flow rate and head will decrease. To adjust the performance of a pump in normal operations, we change the opening degree of the outlet valve of the centrifugal pump. As the valve opening decreases, the system curve becomes more erratic; at this point, the performance curve of the centrifugal pump remains unchanged. Both the pump’s performance curve and the system curve shift upward, resulting in a decrease in the pump’s flow rate and an increase in pressure. The additional pressure at this time overcomes the resistance caused by the small opening degree of the outlet valve. Compared to variable frequency control, adjusting the centrifugal pump’s outlet valve clearly results in higher energy consumption.