Impact of reduced flow rate during pump operation on the pump
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What happens to a pump that is in operation if its flow rate decreases? A decrease in the pump’s flow rate can lead to cavitation; why is this the case?
A decrease in flow rate has no effect on the pump; it’s just like closing the pump’s outlet valve. Your last sentence is incorrect; it’s not a drop in flow rate that causes cavitation, but rather cavitation that leads to a drop in flow rate. If the pressure loss in the pump inlet pipe increases (for example, due to a clogged pump inlet filter), water cannot enter the pump, resulting in cavitation.
As the pump flow rate decreases, the pump will heat up, which can lead to damage to the seals and even shaft failure.
A decrease in flow rate can affect processes such as level control; the causes of this decrease include cavitation and blockages at the inlet
A decrease in flow rate has the main effect of increasing the vibration of the pump, which in turn affects its stable operation over long periods of time. If the flow rate continues to decrease and this situation persists for an extended period, the reduced efficiency of the pump causes mechanical work to be converted into thermal energy within the liquid in the pump, resulting in heating of the liquid. This increases the saturated vapor pressure of the liquid, thereby leading to cavitation ； Regarding the above two points, reference can be made to relevant provisions in API 610 concerning \"minimum pump flow rate\" and \"vibration\", etc.
For long-term operation, it is advisable to keep the pump’s flow rate within the range of 70%-125% of its rated flow rate; this range results in low vibration and high efficiency. The long-term traffic volume should not be lower than 30%; if this cannot be achieved, it is best to use a diversion tube
Cavitation occurs due to an excessive suction lift or too high a liquid temperature; closing the outlet valve will not prevent cavitation.
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When the pump outlet is closed to a level that results in a minimum flow rate, according to the law of conservation of energy, mechanical energy is converted into thermal energy, causing the temperature of the pump casing to rise. The material vaporizes, leading to cavitation, as well as noise and vibrations.
When traffic decreases, first analyze what causes it. Low liquid level in the storage tank, high temperatures leading to cavitation in the pump, blockages at the pump’s inlet and outlet, decreased pump power, and so on. Flow rate has no direct effect on the pump; it is the reasons for the decrease in flow rate that affect the pump. A reduced pump suction volume leads to low flow, which can cause cavitation in the pump and increased vibration. A clogged pump outlet pipeline results in low flow, which causes excessive pressure in the pipeline and can damage the pump itself, the pipelines, and the flanges.