Mechanical Sector [Pump Equipment Version] Daily Question Summary Post

【Daily Question: Pump Equipment】Weekly Summary: https://bbs.hcbbs.com/thread-2165024-1-1.html Monday (2018.11.19): https://bbs.hcbbs.com/thread-2154007-1-1.html What parameters of a centrifugal pump are directly affected by the inlet pressure? (AD) A. Outlet pressure B. Head C. Flow rate D. Cavitation E. Shaft power Tuesday (2018.11.20): https://bbs.hcbbs.com/thread-2155320-1-1.html In the poem “Viewing the Lushan Waterfall” by Tang Dynasty poet Li Bai, there is a line that reads “The waterfall plunges down three thousand feet.” This line indicates: (AD) A. Lushan is at a great altitude, so the water has high potential energy. B. Lushan is at a great altitude, so the water has high kinetic energy. C. The process of kinetic energy being converted into potential energy. D. The process of potential energy being converted into kinetic energy. Wednesday: https://bbs.hcbbs.com/thread-2157096-1-1.html Which of the following statements about self-priming centrifugal pumps is correct? (ACD) A. Under standard atmospheric pressure, the ideal maximum priming height is 10.33 meters. B. A thinner inlet pipeline should be used; a too-thick inlet pipeline prevents priming. C. The priming time is related to the amount of air in the inlet pipeline. D. The priming capacity is directly related to the NPSHr value, and not directly related to flow rate, head, or speed. Thursday (2018.11.22): https://bbs.hcbbs.com/thread-2159390-1-1.html Which of the following statements regarding the balance of axial forces in the rotor system of a centrifugal pump is correct? (AC) A. The double-suction pump design can balance axial forces. B. Pumps with double volute channels can balance axial forces. C. Multi-stage pumps use symmetrically arranged impellers to balance axial forces. D. The radial guide vanes in the flow channels outside the impellers within the pump can balance axial forces. Friday (2018.11.23): https://bbs.hcbbs.com/thread-2161314-1-1.html Which of the following statements about magnetic pumps and shielded pumps is correct? (ABCD) A. Magnetic pumps rely on the magnetic field generated by permanent magnets. B. Shielded pumps rely on the magnetic field generated by windings. C. Both magnetic pumps and shielded pumps are completely leak-free pumps. D. Both magnetic pumps and shielded pumps with metal isolation sleeves suffer from metal eddy current losses. Saturday (2018.11.24): https://bbs.hcbbs.com/thread-2163102-1-1.html If the efficiency of a centrifugal pump is 65%, which of the following statements is correct? (AB) A. An efficiency of 65% means that the medium receives 65% of the shaft power. B. An efficiency of 65% means that 35% of the shaft power is lost. C. An efficiency of 65% means that the medium receives 65% of the motor power. D. An efficiency of 65% means that 35% of the motor power is lost

【Daily Question: Pump Equipment】Weekly Summary https://bbs.hcbbs.com/thread-2165024-1-1.html Monday (2018.11.26) https://bbs.hcbbs.com/thread-2166493-1-1.html A metal flexible diaphragm coupling is a common type of coupling. Which of the following statements is correct? (B) A. The more holes on the diaphragm, the better the coupling’s compensatory ability. B. The more holes on the diaphragm, the greater the torque that can be transmitted. C. The longer the intermediate section (extension section), the worse the coupling’s compensatory ability. D. Vibration reduction by a coupling means that it can eliminate vibrations. Tuesday (2018.11.27) https://bbs.hcbbs.com/thread-2168101-1-1.html The specific gravity of the fluid being transported has a direct impact on which of the following parameters? (CE) A. Flow rate B. Head C. Outlet pressure D. NPSHA E. Shaft power Wednesday (2018.11.28) https://bbs.hcbbs.com/thread-2169949-1-1.html When selecting a pump, which of the following conditions must be met? (ABCDE) A. The pump’s NPSHR must be less than the system’s NPSHA. B. The flow rate must meet the required value. C. The outlet pressure must meet the required value. D. The motor power must not exceed its capacity. E. The material in contact with the fluid must be resistant to corrosion by that fluid. Thursday (2018.11.29) https://bbs.hcbbs.com/thread-2171817-1-1.html Regarding the balance of radial forces in the rotor system of a centrifugal pump, which of the following statements is correct? (BD) A. A double-suction pump can balance radial forces through its double-suction impeller. B. A pump with a double-casing design can balance radial forces. C. Multiple stages in a pump can balance radial forces by arranging the impellers symmetrically. D. The radial guide vanes in the pump’s internal flow channels can balance radial forces. Friday (2018.11.30) https://bbs.hcbbs.com/thread-2173478-1-1.html What factors are directly related to the displacement of a reciprocating pump? (Multiple choice) A. Stroke size B. Size of the safety valve C. Operating frequency D. Cylinder diameter E. Number of cylinders F. Discharge pressure Saturday (2018.12.1) https://bbs.hcbbs.com/thread-2175418-1-1.html The starting methods for the electric motor that drives the pump include (ABC): A. Direct start B. Reduced-voltage start C. Soft start (which can be considered a form of variable-frequency start) D. Quick start

【Daily Question: Pump Equipment】Weekly Summary: https://bbs.hcbbs.com/thread-2193489-1-1.html Monday (2018.12.3): https://bbs.hcbbs.com/thread-2177819-1-1.html The relationship between various performance parameters of a pump exists under the condition that ( ), with the other parameters changing as flow rate changes. Pump manufacturers usually represent these using characteristic curves (performance curves). (D) A. Shaft power B. Head C. Flow rate D. Rotational speed Tuesday (2018.12.4): https://bbs.hcbbs.com/thread-2179645-1-1.html Which of the following statements about pumping units is correct? (C): A. The inlet pipe is generally under positive pressure, while the outlet pipe is under negative pressure. B. Centrifugal pumps installed above the water surface of the inlet tank can be started directly without needing to be filled with water. C. Centrifugal pump units installed above the water surface of the inlet tank must be filled with water before starting. D. Centrifugal pumps must be installed below the water surface of the inlet tank. Wednesday (2018.12.5): https://bbs.hcbbs.com/thread-2180752-1-1.html A centrifugal pump is used to transport clean water at room temperature. Given that the flow rate is 50 m³/h, the head is 32 m, the shaft power is 7.9 KW, the motor power is 11 KW, and the rotational speed is 2950 RPM, then the pump’s efficiency is closest to which of the following values? (B) A. 72% B. 55% C. 52% D. 40% Thursday (2018.12.6): https://bbs.hcbbs.com/thread-2182538-1-1.html The performance parameter values listed on a pump’s nameplate at its designed rotational speed are generally the values obtained when ( ). (F) A. The rotational speed is at its highest B. The flow rate is at its maximum, and the head is at its highest D. The net positive suction head is at its minimum E. The shaft power is at its lowest F. The pump efficiency is at its highest Friday (2018.12.7): https://bbs.hcbbs.com/thread-2184387-1-1.html With all other conditions remaining unchanged, when the specific gravity of the medium transported by the pump decreases, which of the following statements is correct? (A B C I J) A. The flow rate remains unchanged. B. The head remains unchanged. C. The shaft power decreases. D. The outlet pressure remains unchanged. E. The flow rate decreases. F. The shaft power remains unchanged. G. The pump’s net positive suction head decreases. H. The head decreases. I. The outlet pressure decreases. J. The pump’s net positive suction head remains unchanged. Saturday (2018.12.8): https://bbs.hcbbs.com/thread-2192325-1-1.html When a centrifugal pump uses ( ), it results in a decrease in the pump’s flow rate, yet an increase in the pump’s shaft power. (C) A. Variable frequency speed control B. Outlet valve control C. Return bypass pipe control D. Adjustment of the outer diameter of the impeller

【Daily Question: Pump Equipment】Weekly Summary https://bbs.hcbbs.com/thread-2215895-1-1.html Monday (2018.12.10): https://bbs.hcbbs.com/thread-2194393-1-1.html (Multiple-choice question) It is known that a centrifugal pump is used to transport high-concentration methanol solution at room temperature. The specific gravity of methanol is 0.8, the pump’s flow rate is 50 m3/h, the head is 80 m, the inlet pressure is 2 kgf/cm2, the rotational speed is 2900 r/min, and the motor power is 22 KW. Which of the following outlet pressures is closest to the actual value? (B) A 1.0 MPa B 0.84 MPa C 0.64 MPa D 2.64 MPa E 10 kgf/cm2 F 1.2 MPa Tuesday (2018.12.11): https://bbs.hcbbs.com/thread-2199654-1-1.html (Multiple-choice question) A centrifugal pump is used in a coastal area to transport clean water, with the water temperature at 90°C (the saturated vapor pressure of water at 90°C is 70 KPa, and its specific gravity is 0.965). The absolute inlet pressure is 0.08 MPa, and the NPSHR of the pump at its rated flow rate is 3.0 m. Will cavitation occur when this pump operates at its rated point after it is started? (A) A will experience cavitation, and the pump cannot be used. B: Critical cavitation; the pump cannot continue to operate. C: No cavitation will occur, and the pump operates normally. D: Uncertain. Wednesday (2018.12.12): https://bbs.hcbbs.com/thread-2207623-1-1.html (Multiple-choice question) For a double-cylinder, four-acting reciprocating pump, if the assembler misses installing one of the pump valves, then, ignoring the volume of the piston rod, the theoretical flow rate of the pump will (C) A: Not decrease. B: Decrease by 1/2. C: Decrease by 1/4. D: Decrease by 1/8. E: Be zero. Thursday (2018.12.13): https://bbs.hcbbs.com/thread-2211989-1-1.html (Multiple-choice question) In a centrifugal pump, as the viscosity of the fluid being pumped increases, then (ACDF) A: The head decreases. B: The net positive suction head decreases. C: The outlet pressure decreases. D: The efficiency decreases. E: The shaft power decreases. F: The shaft power increases. Friday (2018.12.14): https://bbs.hcbbs.com/thread-2213494-1-1.html (True/False questions) 1. Centrifugal pumps driven by non-voltage-variable motors generally have their flow rate controlled by regulating the valve in the pump’s outlet pipeline. (True) 2. The first step in properly shutting down a ZA series chemical process pump is to cut off the power supply to the motor. (False) Saturday (2018.12.15): https://bbs.hcbbs.com/thread-2214885-1-1.html (True/False questions) 1. Gradual clogging of the filter screen at the inlet of a centrifugal pump, as well as wear and friction of the sealing ring, can cause the motor to operate under light load or overload conditions, respectively. (True) 2. Cavitation in a pump always occurs first at the inlet blades of the first impeller stage. (True)

【Daily Question: Pump Equipment】Weekly Summary https://bbs.hcbbs.com/thread-2225890-1-1.html Monday (2018.12.17) https://bbs.hcbbs.com/thread-2216670-1-1.html 1. Steel grade 45# has a higher carbon content than steel grade 25#, so it possesses better weldability. (Mistake) 2. ZG230-450 is a cast carbon steel material, meaning that its tensile strength ranges from 230 MPa to 450 MPa. (Mistake) Tuesday (2018.12.18) https://bbs.hcbbs.com/thread-2217899-1-1.html 1. If the outlet valve of the centrifugal pump is gradually opened from fully closed to its maximum position, the following conditions may occur: flow rate can be zero, efficiency can be zero, and the net positive suction head can be zero. (Mistake) 2. Based on the variation pattern of the pump’s flow-rate vs. shaft power curve, it can be determined whether the pump should be started with the valve closed or open. (Correct) Wednesday (2018.12.19) https://bbs.hcbbs.com/thread-2220199-1-1.html 1. The NPSH values for centrifugal pumps are all less than 10.3 meters. (Mistake) 2. Increasing the flow velocity of the liquid at the inlet of the centrifugal pump can reduce the tendency of the pump to experience cavitation. (Mistake) Thursday (2018.12.20): https://bbs.hcbbs.com/thread-2221393-1-1.html 1. The main difference in the chemical composition of 304 and 316L metals is that, at the same carbon content, their levels of other chemical elements such as Cr and Ni differ. (Mistake) 2. For impellers with a large outlet diameter, it is necessary to cut them at an angle along the outer diameter; this is done so that the impeller can still maintain axial force balance and good dynamic balance after cutting. (Mistake) Friday (2018.12.21): https://bbs.hcbbs.com/thread-2223085-1-1.html 1. The factory testing items for ordinary centrifugal pumps include three aspects: performance tests, vibration tests, and temperature rise tests. (Mistake) 2. The operating pressure of a pump is limited by the hydrostatic test pressure of its pump casing; the maximum operating pressure must not exceed this value. (Mistake) Saturday (2018.12.22): https://bbs.hcbbs.com/thread-2224434-1-1.html 1. For the motor used in conjunction with a pump, the actual electricity consumption equals the motor’s rated power multiplied by the operating time. (Mistake) 2. For a given pump and fixed operating conditions, using a motor with a lower rated power will definitely result in less energy consumption. (Mistake)

This post was last edited by tianyewei on 2018-12-29 at 11:21. Monday (2018.12.24): 1. The vaporization pressure of a liquid is an absolute pressure value. (Correct) 2. The vacuum level at the pump inlet is the absolute pressure difference. (Correct) Tuesday (2018.12.25) https://bbs.hcbbs.com/thread-2228200-1-1.html 1. For media that are prone to crystallization or polymerization, a filter screen should be installed at the pump inlet. (Incorrect) 2. From the perspective of ease of maintenance, check valves should be located upstream of the pump outlet valve. (Correct) Wednesday (2018.12.26) https://bbs.hcbbs.com/thread-2229368-1-1.html 1. API610 specifies that there should be a hardness difference of at least HB100 between the impeller seal ring and the pump body seal ring, in order to prevent them from engaging with each other due to similar hardness levels. (Incorrect) 2. The only purpose of quenching and tempering carbon steel shafts is to increase their surface hardness. (Incorrect) Thursday (2018.12.27) https://bbs.hcbbs.com/thread-2230739-1-1.html 1. Is the pump efficiency the ratio of useful power to shaft power? (Correct) 2. The value of the cavitation specific speed is independent of the outlet parameters of the pump; the higher the cavitation specific speed, the better the pump’s resistance to cavitation. (Correct) Friday (2018.12.28) https://bbs.hcbbs.com/thread-2232802-1-1.html 1. If the flow condition of the fluid in the pipeline is stable, the pressure gauge can be connected to a straight pipe section of any diameter near the pump outlet in order to measure the actual outlet pressure of the pump. (Incorrect) 2. The pressure gauge can function properly as long as the actual operating pressure is below its range. (Incorrect) Saturday (2018.12.29) https://bbs.hcbbs.com/thread-2235019-1-1.html 1. Cavitation occurs in all devices used for transporting liquids, including both static and dynamic devices. (Correct) 2. Common torque wrenches control the upper limit value of the tightening torque (Incorrect)

I’m extremely busy at the end of this month; I hardly have any time to handle management tasks. If you have time, please help summarize it:handshake

Monday (2018.12.24) https://bbs.hcbbs.com/thread-2226803-1-1.html 1. The vaporization pressure of a liquid is an absolute pressure value. (Yes) 2. The pump inlet vacuum is the absolute pressure difference. (Tue) December 25, 2018: https://bbs.hcbbs.com/thread-2228200-1-1.html 1. For media that are prone to crystallization or polymerization, a filter screen should be installed at the pump inlet (False). 2. From the perspective of ease of maintenance, a check valve should be located upstream of the pump outlet valve (True). Wed) December 26, 2018: https://bbs.hcbbs.com/thread-2229368-1-1.html 1. API610 stipulates that there should be a hardness difference of at least HB100 between the impeller seal ring and the pump body seal ring, in order to prevent them from grinding against each other due to similar hardness levels. (Incorrect) 2. The only purpose of quenching and tempering carbon steel shafts is to increase their surface hardness. (Yes) Thursday (2018.12.27) https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=2230739 1. Is the efficiency of a pump the ratio of useful power to shaft power? (Yes) 2. The value of the cavitation specific speed is independent of the pump’s outlet parameters; the higher the cavitation specific speed, the better the pump’s resistance to cavitation. (F) Friday (2018.12.28) https://bbs.hcbbs.com/thread-2232802-1-1.html 1. If the flow condition of the fluid in the pipeline is stable, the pressure gauge can be connected to a straight pipe section of any diameter near the pump outlet in order to measure the actual outlet pressure of the pump. (Wrong) 2. The pressure gauge can function properly as long as the actual operating pressure is below its range. (Wrong) Saturday (2018.12.29) https://bbs.hcbbs.com/thread-2235019-1-1.html 1. Cavitation is a common phenomenon in any device used for transporting liquids, whether it is a static or dynamic device. (Correct) 2. Common torque wrenches control the upper limit value of the tightening torque (Incorrect)

Monday (2018.12.31) https://bbs.hcbbs.com/thread-2238671-1-1.html 1. In our country, the higher failure rate of equipment in winter compared to summer is mainly due to the low temperatures in winter. (True) 2. The function of a reducer is to enable a smooth transition in area between pipes of different diameters. (True) Tuesday (2019.1.1) https://bbs.hcbbs.com/forum.php? ... ;extra=#pid21554045 I took myself a day off for New Year’s Day, haha... Wednesday (2019.1.2) https://bbs.hcbbs.com/thread-2240821-1-1.html 1. The mechanism for balancing the axial force of a pump: Similar to a balance disc, it has an axial clearance, so it can automatically adjust and balance the axial thrust when the pump shaft moves axially. (False) 2. The greater the deviation of the pump’s flow rate from the design value, the greater the radial force on the impeller. (True) Thursday (2019.1.3) https://bbs.hcbbs.com/thread-2242216-1-1.html 1. There are three most common reasons for excessive vibration in pumps: the pump operating far away from its optimal operating point or having a tendency to cavitate, poor fixation of the base and pipelines, and poor alignment of the couplings. (True) 2. Like high-speed pumps, multi-stage pumps should have their outlet valves slightly opened at startup, in order to prevent excessive heating due to vigorous mixing inside the pump and to allow any gas formed by the vaporization of the fluid to escape. (True) Friday (2019.1.4) https://bbs.hcbbs.com/thread-2248182-1-1.html 1. Compared to plum blossom-shaped elastic rubber (claw-type) couplings, diaphragm couplings have greater compensatory capacity, but their temperature resistance is lower. (False) 2. The reason why centrifugal pumps can only transport liquids and not gases is that liquids have a higher density; they are subjected to greater centrifugal force due to the rotation of the impeller, which allows sufficient negative pressure to be created at the inlet, enabling liquid to continuously flow into the pump’s inlet. (Yes) Saturday (2019.1.5) https://bbs.hcbbs.com/thread-2249684-1-1.html 1. The greater the absolute difference between the pH value of the medium transported by the pump and 7, the stronger the corrosiveness of that medium (Wrong). 2. The shorter the inlet pipe of a centrifugal pump, the better; therefore, elbows should be connected directly to the pump inlet (Wrong)