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Common flow regulation methods for centrifugal pumps: Centrifugal pumps are widely used in industries such as water management and chemicals, and there is an increasing emphasis on selecting the appropriate operating conditions for them as well as analyzing their energy consumption. Typically, the flow rate and head of a centrifugal pump may not match those of the piping system; or due to changes in production tasks or process requirements, it is necessary to adjust the pump’s flow rate, which essentially means changing the operating point of the centrifugal pump. In addition to the correctness of the centrifugal pump selection during the engineering design phase, the choice of operating conditions when the pump is actually in use also directly affects the user’s energy consumption and costs. Therefore, it is particularly important to know how to reasonably change the operating point of the centrifugal pump. The working principle of a centrifugal pump is to convert the mechanical energy generated by the high-speed rotation of the electric motor into the kinetic and potential energy of the liquid being pumped, which is a process of energy transfer and conversion. Based on this characteristic, it can be seen that the operating point of a centrifugal pump is determined by the balance between the energy supply and demand in the pump and pipeline system; whenever there is a change in either of these elements, the operating point will shift. Changes in the operating condition points are caused by two factors: 1. Changes in the characteristic curve of the water pump itself, such as impeller cutting. 2. Changes in the characteristic curve of the piping system, such as valve throttling. The following analyzes and compares these two methods: 1. Impeller cutting When the rotational speed remains constant, both the head and flow rate of the pump are related to the diameter of the impeller. For pumps of the same model, the cutting method can be used to modify their characteristic curves. Let the original impeller diameter of the centrifugal pump be D, its flow rate be Q, its head be H, and its power be P. The diameter of the impeller after cutting is D’, its flow rate is Q’, its head is H’, and its power is P’. The relationships between these values are as follows: The above three equations are collectively referred to as the laws of impeller cutting for pumps. The cutting law is based on a large amount of empirical experimental data; it states that if the amount of cutting by the impeller is kept within certain limits (with these limits being related to the specific speed of the water pump), then the efficiency of the water pump before and after cutting can be considered constant. Impeller cutting is a simple and effective method for altering the performance of water pumps; it is what is known as diameter adjustment. To a certain extent, it resolves the conflict between the limited range of pump types and specifications and the diverse requirements of different water supply applications, thereby expanding the scope of use for water pumps. Of course, impeller cutting is an irreversible process, and users must conduct precise calculations and assess the economic viability before proceeding with it. II. Valve throttling: The simplest way to change the flow rate of a centrifugal pump is to adjust the opening degree of the pump’s outlet valve, while keeping the pump’s rotation speed constant (usually at the rated speed). Essentially, this involves changing the position of the pipeline’s characteristic curve in order to alter the pump’s operating point. When the valve is closed to control the flow rate, the water supply capacity of the pump itself remains unchanged, as does its head characteristic; however, the pipe resistance characteristic changes as the valve opening degree changes. This method is easy to operate, provides a continuous flow rate, and can be adjusted freely between a maximum flow rate and zero, without requiring any additional investment; it is suitable for a wide range of applications. However, throttling regulation relies on consuming the excess energy of the centrifugal pump to maintain a certain supply volume, which reduces the efficiency of the pump as well; hence it is not economically viable. Currently, impeller cutting is the preferred method for adjustment among many companies, as it helps to save energy and reduce consumption. However, before carrying out impeller cutting, precise calculations must be done first to ensure that the resulting impeller will meet the required operating conditions.