Abstract : This paper discusses some problems in the control and operation of water pumps during the water supply process of waterworks, and studies the applicability and economy of closed-loop variable frequency speed control system in the water supply industry to achieve an energy-saving production mode of automatic operation. Keywords : PLC; frequency converter; flow rate; closed-loop variable frequency regulation 1 Introduction With the increasing urbanization level in China, the urban water supply industry has been under great pressure. The existing water supply system, technical equipment and operation mode are difficult to guarantee the safety of urban water supply networks and cannot meet people's demand for water flow. The development of waterworks themselves also requires the realization of automation and unmanned operation of water supply to achieve the requirements of energy saving, consumption reduction, high efficiency and reliability. Because the flow rate and pressure of the pipeline system change according to the water consumption, if the water pump unit operates at a constant speed, the system water supply pressure changes with the water supply flow rate. When the flow rate decreases, the water supply pressure increases, and vice versa. This situation is exactly the opposite of the water supply requirements. This relationship between flow rate and pressure is an important cause of system energy waste and pipe bursts. Furthermore, with the increase in high-rise buildings in cities, the municipal water supply network is experiencing insufficient pressure. For taller buildings, localized pressurized water supply—a towerless water supply system—must be adopted. The key technology to solve these problems is how to effectively implement closed-loop variable frequency control of the pump sets. 2. Problems with Current Pump Control Systems Currently, most water plants use a pump system with one variable frequency speed-regulating pump and several fixed frequency constant speed pumps operating in parallel. Dispatchers, based on data from pressure monitoring points distributed throughout the city's water supply network, instruct the water plant to manually adjust the inverter output frequency to a certain level or switch the number of fixed frequency pump sets. This control method has the following problems: (1) Due to changes in seasons, weather, and production needs, the demand for water fluctuates greatly (too low a water pressure will not meet the requirements, while too high a water pressure will cause energy waste); (2) The water supply pressure varies greatly; (3) Due to the large fluctuations in water consumption, operators need to start and stop the pump sets as needed at any time, and manually optimize the combination of the number of pumps in operation; frequent start-ups and shutdowns of the pump sets cause large fluctuations in water pressure, which has a significant impact on the service life of the motor and the pipeline network; [b][align=center]For more details, please click: Energy-saving control of water pumps in water supply systems[/align][/b]