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Monday (2019.6.10) https://bbs.hcbbs.com/thread-2724503-1-1.html 1. In multi-stage pumps, the inlet diameters of all the impellers (single-suction type) are the same (incorrect – the inlet diameter of the first-stage impeller is larger, in order to reduce the net positive suction head)； 2. Centrifugal pumps with a fixed specific speed all have an upper limit to their efficiency (correct). Tuesday (2019.6.11) https://bbs.hcbbs.com/thread-2725077-1-1.html 1. The blades of centrifugal pump impellers with narrow flow channels (low specific speed) are cylindrical in shape, not twisted; the main reason for this is the narrow flow channel, as twisted blades do not contribute much to improving efficiency. (Mistake – due to the narrow flow channels, it is difficult to cast twisted blades, and casting defects are likely to occur.) 2. The flow area of the impeller’s flow channels in a centrifugal pump remains essentially constant from the inlet to the outlet of the blades. (Error–gradually increasing) Wednesday (2019.6.12): https://bbs.hcbbs.com/thread-2726007-1-1.html. 1. The vertical distance from the center line of the suction pump inlet to the water tank is 5 meters; the loss in the suction pipe is 0.2 meters, and the combined loss due to the inlet valve and elbow is 0.3 meters. Under standard atmospheric pressure and normal temperature conditions, for the pump to be able to operate properly, its NPSHR must be no greater than (10.3 – 0.2 – 0.3 – 5 – 0.5 = 4.3) meters. 2. The impeller of the centrifugal pump has a diameter of 310 mm and rotates at 2950 RPM; therefore, the linear velocity at the outer diameter of the impeller is (2950*0.31*3.14159/60 = 47.88) m/s. Thursday (2019.6.13) https://bbs.hcbbs.com/thread-2726522-1-1.html 1. Fill in the blanks: The single-stage, single-suction, cantilevered horizontal centrifugal pump uses a mouth ring + balance hole design to balance the axial force. The pressure at the pump inlet is 0 MPa(A); the inner diameter of the pump cover’s mouth ring is 220 mm, while the outer diameter of the rear mouth ring of the impeller is 219.4 mm. The impeller has 5 blades, so the diameter of each balance hole on the impeller should be (18 – area of the gap ring band behind the rear mouth ring × 6) / 5 holes, in millimeters ； 2. Judgment: Jet pumps do not fall under the category of positive displacement pumps (correct). Friday (2019.6.14) https://bbs.hcbbs.com/thread-2727111-1-1.html 1. The mechanical losses, volumetric losses, and hydraulic losses in centrifugal pumps are collectively referred to as the pump’s overall efficiency (incorrect) ； 2. At a grid frequency of 60Hz, the synchronous speed of a 2-pole Y-type motor is 3600 r/min (correct). Saturday (2019.6.15) https://bbs.hcbbs.com/thread-2727560-1-1.html In a straight water conveyance pipeline, the water flow is steady and constant; the diameter at the inlet is larger than that at the outlet, and the pressure at the inlet is higher than that at the outlet. If the pressure difference between the inlet and outlet is converted into a water column height of H meters, then which of the following statements is correct? (BD – In addition to losses, an increase in flow velocity also leads to a decrease in pressure.) A. The total loss in the straight pipeline is H meters. B. The total loss in the straight pipeline is less than H meters. C. The total loss in the straight pipeline is greater than H meters. D. The flow velocity at the outlet is higher than that at the inlet. Have a pleasant weekend! Happy Father’s Day! !