Replace the centrifugal pump with one of higher flow rate without changing the pipe size

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When our factory was first established, the warm water system used centrifugal pumps of the KQW150/460-75/4 (Z) series manufactured by the Kaiquan Group; these pumps had a flow rate of 200 m3/h and a head of 80 m. Three such pumps were in use, with two operating simultaneously while one served as a backup pump. The current consumption was between 110 and 120 A. The outlets of the warm water pumps were combined together before being routed to two plate heat exchangers – one for cooling the water to 40 degrees and the other to 45 degrees – from where it was then sent to respective pipelines for insulation or further cooling. The pipe diameter of the outlet pipe from the warm water tank is DN300; it narrows to DN200 at the point where it connects to the pump. The pump’s outlet pipe also has a diameter of DN200, which then narrows to DN300 before reaching the plate heat exchanger, where it further narrows to DN100 and DN300. Due to the increased production capacity, the flow rate is insufficient; therefore, the original three warm water pumps have been replaced with KQW200/460-110/4 (Z) models (with a capacity of 300 m3/h and 80 m pressure). At the 40-degree warm water side, a flow meter shows a flow rate of around 540 m3/h (there are still a few devices without flow meters, so the actual flow rate is likely higher than this). In winter, the flow in some 45-degree pipes is poor, resulting in stagnant water. Therefore, it is planned to replace one of the KQW200/460-110/4 (Z) pumps (with a capacity of 300 m3/h and a head of 80 m) with a KQW200/400-75/4 (Z) pump (with a capacity of 400 m3/h and a head of 50 m). This new pump will be used to supply water at 40 degrees Celsius; a valve will be installed at its outlet to isolate it from the other two pumps. The original two pumps will continue to supply water at 45 degrees Celsius, with one pump in use and the other as a backup. Will it be possible to meet the flow requirements for water at 40 degrees Celsius without changing the diameter of the existing pipes? If it cannot meet the requirements, please recommend a more suitable model.