★Specialized Examination for Chemical Engineering ★ — One question per day (2016-1-5) — Points are awarded for participation
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This post was last edited by zshiwei2008 on 2016-1-19 09:48. Points system for the daily question: Participation – 1~3 points; Correct answer – 5 points; In-depth analysis – 5~10 points. The answer is provided the next day. Due to limited capabilities, I am unable to provide more in-depth explanations for each question; therefore, on the second day, in addition to offering reference options, I will also remove the restriction on reading replies. I hope that all candidates can learn from one another and improve together! I’ve been quite busy with work lately, so I can’t guarantee that I’ll be able to create questions on a daily basis. Moreover, I still haven’t found a suitable set of questions. If anyone has a good source of questions, please share some information. Daily Question (2016-1-5): 1. Shortly after starting a certain centrifugal pump, it was observed that the vacuum level at the pump’s inlet gradually dropped to zero, and the pressure gauge at the outlet also dropped to zero. At this point, the centrifugal pump was no longer able to pump any water. Determine which of the following is the cause of the failure? A. Forgetting to water it B. Clogged intake pipeline C. Clogged discharge pipeline D. Air leakage in the intake pipeline. Answer: D. Real exam question from 2011
1. Shortly after a certain centrifugal pump was started, it was observed that the vacuum level at the pump’s inlet gradually dropped to zero, and the pressure gauge at the pump’s outlet also dropped to zero; at this point, the centrifugal pump was no longer able to pump any water out. Determine which of the following is the cause of the failure? A、DA: Forgot to water. B、Blockage in the suction line. C、Blockage in the discharge line. D、Leak in the suction line
D. After the pump starts up, the inlet vacuum becomes zero, indicating that the negative pressure inside the pump casing has dropped to zero; the outlet pressure also becomes zero, which means no fluid is being forced out. Therefore, there is an air leak at the inlet, and the pump is running idle. Support the event!
First, consider option A: if watering is forgotten, it’s possible that no water will be delivered. In that case, the pressure gauge on the outlet pipe will read 0, which clearly does not match what is stated in the question. Option B: if the suction pipeline is blocked, the reading on the vacuum gauge will not become 0. Option C: if the outlet pipeline is blocked, both the vacuum gauge and the pressure gauge will have readings. The correct answer is D – only if there is a leak in the suction pipeline will both the vacuum gauge and the pressure gauge read 0. This is because the leak allows air from the outside atmosphere to enter the suction pipeline, resulting in a vacuum gauge reading of 0; no water can be delivered, and therefore there will be no water in the outlet pipe as well, with the pressure gauge also reading 0
1. Shortly after a certain centrifugal pump was started, it was observed that the vacuum level at the pump’s inlet gradually dropped to zero, and the pressure gauge at the pump’s outlet also dropped to zero; at this point, the centrifugal pump was no longer able to pump any water out. Determine which of the following is the cause of the failure? A、DA: Forgot to water. B、Blockage in the suction line. C、Blockage in the discharge line. D、Leak in the suction line
If it is B, the import vacuum level will increase