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This post was last edited by 3983596_FPPZ on 2019-2-17 at 22:19. Friday (2019.2.8): https://bbs.hcbbs.com/thread-2287342-1-1.html For a centrifugal pump operating at its rated flow rate – with a flow rate of 110 m3/h, head of 85 m, efficiency of 65%, and rotational speed of 2900 rpm – the shaft power required to convey water at normal temperature is (39.2) kW, while the power required for the motor is (45) kW. Saturday (2019.2.9): https://bbs.hcbbs.com/thread-2288013-1-1.html On the performance curves of common centrifugal pumps, the flow-rate vs. efficiency curve shows an increase at first, followed by a decrease, reaching its maximum value at the rated flow rate; whereas the flow-rate vs. shaft power curve shows a monotonic increase. Sunday (2019.2.10): https://bbs.hcbbs.com/thread-2288754-1-1.html Briefly explain why pumps of the OH2 type as specified in API610 standards (horizontal pumps with pump supports and centered support) can be used in high-temperature conditions Answer: Under high-temperature conditions, the pump body, which is supported by a structure along its central axis, expands upward and downward due to heat expansion, while the position of the axis around which it rotates remains essentially unchanged. The alignment of the couplings is not affected by changes in operating temperature, and the stress on the shaft remains roughly constant; for these reasons, this design is often used in high-temperature applications. Monday (2019.2.11): https://bbs.hcbbs.com/thread-2289143-1-1.html. Briefly explain why, at zero flow rate (the closed position), the shaft power, according to the formula for calculating shaft power, is not zero Answer: 1. The shaft power formula is calculated based on the ratio of useful power to efficiency. When the flow rate is zero, the useful power is zero and so is the efficiency; therefore, efficiency cannot be used as a denominator in the formula, and this formula is not applicable when the flow rate is zero. 2. When the flow rate is zero, all of the power is consumed in unnecessary losses (hydraulic losses, volumetric losses, mechanical losses, etc.), so the shaft power is not zero at this time. Tuesday (2019.2.12) https://bbs.hcbbs.com/thread-2290585-1-1.html Why can’t high-speed pumps be started with the outlet valve closed? Answer: When a high-speed pump is operating at high speed, the rotor spins very fast. When the outlet valve is closed, the liquid cannot flow out, and the medium being transported circulates back and forth inside the pump. This causes the temperature to rise rapidly, and under such conditions the medium is prone to vaporization, leading to cavitation or a reduction in flow rate, which can result in damage to the pump! Wednesday (2019.2.13) https://bbs.hcbbs.com/thread-2292066-1-1.html: It is a single-stage centrifugal pump with a designed head of 47 m, an impeller diameter of 202 mm, and a rotational speed of 2900 r/min. The actual measured head was 51 m. According to the proportionality law, the diameter of the impeller after modification would be 194 mm; as a result, the efficiency of the pump decreases slightly (please indicate whether it decreases, increases, or remains unchanged). Thursday (2019.2.14) https://bbs.hcbbs.com/thread-2293322-1-1.html: Pumps with an outlet volute that has an annular flow channel have a flow pattern in which the fluid velocity increases circumferentially from the baffle to the outlet. The efficiency of such pumps is lower than that of pumps with a spiral-shaped outlet volute. Friday (2019.2.15) https://bbs.hcbbs.com/thread-2294715-1-1.html The greater the inlet flow velocity of the impeller in a centrifugal pump, the higher the pump’s NPSHR value will be. This is the main reason why the NPSHR value of high-flow centrifugal pumps is generally high. Saturday (2019.2.16) https://bbs.hcbbs.com/thread-2296208-1-1.html The performance curve of a centrifugal pump includes curves showing the relationship between flow rate and head, efficiency, NPSHR, and shaft power. Briefly explain which curves change when only the specific gravity of the fluid increases, and how they change. Answer: The flow-rate–shaft power curve increases in a linear proportion to the increase in specific gravity, while the other curves remain unchanged