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Pump selection should follow a set of general guidelines to ensure efficiency, reliability, and long-term performance. First, it is essential to choose low-noise, energy-efficient pumps and avoid using outdated or obsolete models. This helps in reducing operational costs and environmental impact.
Second, the pump should be selected based on actual flow and head requirements. It's important to account for potential performance degradation due to wear and tear over time. Therefore, the calculated head should be increased by 5% to 10% to ensure adequate capacity. Pumps should ideally operate within their high-efficiency range. It is generally not recommended to use pumps with a rising section of the QH curve unless they are operated in parallel, which requires careful planning.
Third, when selecting pumps for water tanks or water towers, the number of units should be minimized, with one unit kept as a backup. If a single pump can meet the demand, it is not advisable to operate more than one pump in parallel. If multiple pumps must be used in parallel, the models and sizes should be similar, typically no more than two different models, and the head range should be close. Each pump in parallel should still function within its high-efficiency zone to maintain optimal performance.
Fourth, if frequency control is used for feed pumps, several conditions must be met. The power supply should be reliable, ideally with dual power or dual-loop supply. The most unfavorable operating point should fall at the right end of the pump’s high-efficiency curve, and the variable speed range should stay within this efficient area as much as possible. The pump speed should remain between 75% and 100% of its rated speed. In cases of uneven water supply or large flow variations, multiple pumps may be combined—usually no more than three to four units—with some controlled via frequency and others running at constant speed. A small flow pump and a pressure tank should also be included to manage fluctuations.
Additionally, the system should include water level control. An ultra-high water level alarm should trigger automatic shutdown when the level reaches the design upper limit, and the pump should restart automatically once the water level returns to normal.
Lastly, the equipment should include both a working pump and a spare pump, with the spare capable of handling the maximum water supply capacity of the running pump. The pumps should automatically switch and alternate operation to ensure even wear and extended lifespan. Furthermore, all motors equipped with pumps should have matching pressure ratings to prevent imbalances and ensure smooth operation.