【Q&A Question 162】2017.06.11
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This post was last edited by 955559 on 2017-7-21 23:12. [Q&A Question 162] 2017.06.11: What consequences can arise from using the inlet valve of a centrifugal pump to regulate flow? Why? The reference answers can be seen after *responding*; points are awarded for identifying the key aspects. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) It is not possible to reduce the flow rate by closing the pump’s inlet valve, as this can lead to cavitation. The pump has a certain allowable cavitation head; closing the inlet valve increases the fluid resistance at the inlet, which in turn raises the suction vacuum level and increases the risk of cavitation. Scoring criteria: 2 points for an incorrect answer; 3–8 points for an incomplete answer; 10 points for a correct answer accompanied by a detailed explanation; 15–20 points for a correct answer with additional supplementary information. Please score according to these criteria. Note: If there are editing records after answering, only those who participated will be given points. For continuous malicious spamming, 2 points will be deducted each time, with no upper limit. Pure numbers, pure emojis, or random letters unrelated to the answer are all considered malicious spamming; points will start to be deducted after three warnings. 2017 Q&A Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657793-1-1.html 2017 Daily Question Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657794-1-1.html 2016 Q&A Summary Thread (updates completed) http://bbs.hcbbs.com/thread-1597792-1-1.html
Pump cavitation, insufficient flow rate, prone to cavitation
Because if the pump’s suction inlet is reduced in size, the amount of liquid supplied to the pump will be insufficient, causing the impeller to operate with insufficient fluid and thereby reducing the vacuum level; as a result, the pump will be unable to draw in liquid. Cavitation may also occur when controlling the pump’s inlet valve
Reducing the flow rate by closing the pump’s inlet valve is not a viable approach, as this can lead to cavitation. The pump has a certain allowable cavitation head, and closing the inlet valve increases the fluid resistance at the inlet, which in turn raises the suction vacuum level and increases the likelihood of cavitation occurring
The flow rate is regulated using imported valves; when the flow rate approaches the pump’s minimum value, severe cavitation and vibration occur, which is detrimental to the equipment.
Cavitation will occur, and adjusting the inlet valve will cause the pump to operate at a low load, affecting its head. And cavitation is formed, damaging the impeller.
The centrifugal pump does not deliver sufficient flow, the pump shaft heats up, and there is insufficient suction at the pump inlet
Cavitation occurs because the pump’s allowable cavitation head is fixed; closing the valve at the inlet increases the fluid resistance there, which in turn raises the suction vacuum level and makes cavitation more likely to occur.
If the flow rate is adjusted using the pump’s inlet, it not only fails to maintain the pump’s pressure but also prevents the pump from discharging fluid, and may even cause vaporization that damages the pump body. The reason is that when the inlet valve is adjusted, there is insufficient fluid supply within the pump, which creates a relative negative pressure; as a result, cavitation occurs on the blades of the pump impeller, affecting its performance.
Cavitation occurs when the inlet flow rate is insufficient, leading to cavitation in centrifugal pumps