What Are The Adjustment Methods For The Working Point Of Centrifugal Pumps
Jul 26, 2025
Centrifugal pump is a universal fluid machinery widely used in chemical pump industrial systems. It has many advantages, including a wide range of performance adaptability (including flow rate, pressure head, and adaptability to the properties of the conveying medium), small size, simple structure, easy operation, and low operating costs. Usually, the flow rate and pressure head of the selected centrifugal pump may not be consistent with the requirements in the pipeline, or due to changes in production tasks and process requirements, it is necessary to adjust the flow rate of the pump, which essentially changes the working point of the centrifugal pump. The working point of a centrifugal pump is determined by both the pump's characteristic curve and the pipeline system's characteristic curve. Therefore, changing either characteristic curve can achieve the purpose of flow regulation. At present, the flow regulation methods of centrifugal pumps mainly include regulating valve control, variable speed control, and parallel and series regulation of pumps. Due to the different principles of various adjustment methods, they have their own advantages and disadvantages
1. Change the pipeline characteristic curve
The simplest way to change the flow rate of a centrifugal pump is to use the opening of the pump outlet valve to control it, which essentially changes the position of the pipeline characteristic curve to change the working point of the pump.
2. Change the characteristic curve of centrifugal pump
According to the laws of proportionality and cutting, both methods of changing the pump speed and changing the pump structure (such as cutting the outer diameter of the impeller method) can alter the characteristic curve of a centrifugal pump, thereby achieving the goal of adjusting the flow rate (while changing the pressure head). However, for pumps that are already in operation, changing the pump structure is not very convenient, and due to the change in pump structure, the universality of the pump is reduced. Although it is economically convenient to adjust the flow rate at some times, it is rarely used in production. Here we only analyze the methods of adjusting the flow rate by changing the speed of the centrifugal pump. From Figure 1, it can be analyzed that when the pump speed is changed to adjust the flow rate from Q1 to Q2, the pump speed (or motor speed) decreases from n1 to n2. At a speed of n2, the characteristic curve Q-H of the pump intersects with the pipeline characteristic curve He=H0 G1Qe2 (the pipeline characteristic curve does not change) at point A3 (Q2, H3), which is the new operating point after adjusting the flow rate through speed regulation. This adjustment method has obvious, fast, safe and reliable adjustment effects, which can extend the service life of the pump, save electricity. In addition, reducing the speed of operation can effectively reduce the NPSHr of the centrifugal pump, keep the pump away from the cavitation zone, and reduce the possibility of cavitation in the centrifugal pump. The disadvantage is that changing the speed of the pump requires the use of frequency conversion technology to change the speed of the prime mover (usually the electric motor), which is complex in principle, requires a large investment, and has a small range of flow regulation.
3. Series and parallel adjustment methods of pumps
When a single centrifugal pump cannot meet the conveying task, parallel or series operation of centrifugal pumps can be used. Using two centrifugal pumps of the same model in parallel, although the pressure head does not change significantly, increases the total conveying flow rate, and the overall efficiency of the parallel pump is the same as that of a single pump; When centrifugal pumps are connected in series, the total pressure head increases and the flow rate does not change significantly. The overall efficiency of the series connected pumps is the same as that of a single pump.