【One Question per Day】Weekly Summary 2019.3.24

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Monday (2019.3.18) https://bbs.hcbbs.com/thread-2352477-1-1.html Briefly describe the structural advantages and disadvantages of horizontal split-case pumps (such as BB1, BB3 in API610) compared to radially split pumps (such as OH1, BB2 in API610) Answer: Advantages: 1. The horizontally split pump rotor is easy to disassemble and assemble, making maintenance simpler ； 2. With a separate housing design, it is easy to cast the flow channels; complex channel shapes can be designed, resulting in fewer casting defects. Disadvantages: 1. High precision is required for planar processing at the upper and lower sections, making the processing difficult ； 2. It is difficult to achieve static sealing at the balanced sealing surface when combining upper and lower elements ； 3. The positioning accuracy of the end flanges is slightly poor ； 4. The weight of the hydraulic components in the housing is high. On Tuesday (2019.3.19), https://bbs.hcbbs.com/thread-2353680-1-1.html The reading of the vacuum pressure gauge at the pump inlet was -0.04 MPa; therefore, the vacuum level here is (0.04) MPa, while the absolute pressure is (0.06) MPa. On Wednesday (2019.3.20), https://bbs.hcbbs.com/thread-2357268-1-1.html, it is common to see that the material of bolts in fasteners is A2-70. Here, A2 refers to the second group of austenitic steel materials, usually referring to 304, while 70 denotes the grade of the material’s mechanical properties; this number is 1/10 of the nominal tensile strength, meaning the tensile strength is 700 N/mm². Thursday (2019.3.21) https://bbs.hcbbs.com/thread-2358736-1-1.html Briefly describe the advantages and disadvantages of centrifugal pump impellers with a large number of blades compared to those with a small number of blades Answer: 1. It affects the flow pattern between the blades; the more blades there are, the more stable the flow becomes, tending toward laminar flow, while fewer blades result in turbulent flow. Additionally, the backflow from the working surface to the back side at the blade exit increases hydraulic losses ； 2. It affects the contact area; the more blades there are, the larger the contact area between the liquid and the blades, and thus the greater the wear loss, while less wear occurs in contrast ； 3. It affects the degree of crowding at the inlet; the more blades there are, the greater the crowding at the impeller inlet, which results in a smaller flow area and a worse net positive suction head. Conversely, a better net positive suction head is achieved ； 4. It affects the connection strength; the more blades there are, the greater the strength of the connection between the front and rear covers, which is particularly suitable for high-speed pumps. Conversely, the strength is lower, making the component more prone to damage, especially due to the material used ； 5. It affects casting: the large number of blades and narrow flow channels make casting difficult, resulting in many casting defects ； 6. A larger number of blades enables sufficient work performance, which can slightly increase the head pressure, but the improvement is limited. In short, each type of pump has an optimal number of blades; too many or too few have negative effects. Friday (2019.3.22) https://bbs.hcbbs.com/thread-2360206-1-1.html 1. The output current signal range for common sensors is (4-20) mA, which is a standard used internationally ； 2. Common austenitic stainless steels: 304 and 304L, 316 and 316L; compared to the grades without an “L”, those with an “L” contain less carbon. Saturday (2019.3.23) https://bbs.hcbbs.com/thread-2365099-1-1.html 1. Compared to 304, 316 contains the element (molybdenum) in its chemical composition ； 2. As the flow rate of the centrifugal pump increases, the flow velocity of the liquid inside the pump gradually (increases); the frictional losses caused by this flow velocity gradually (increase) as well, the mechanical efficiency of the pump gradually (decreases), while the overall efficiency of the pump shows an (uncertain trend). Happy weekend! !