【Daily Question: Pump Equipment】Weekly Summary 2019.3.10

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Monday (2019.3.4) https://bbs.hcbbs.com/thread-2319967-1-1.html On a certain pump diagram, the rolling bearing is marked as ”7311B/DB” – what does this mean? Answer: 7311 — Single-row angular contact ball bearing, outer diameter 120mm, inner diameter 55mm, width 29mm ； B – The bearing contact angle is 40 degrees (the larger the contact angle, the greater the capacity to withstand axial loads) ； DB – Two single-row bearings installed back to back (face-to-face installation: DF; series installation: DT). Tuesday, March 5, 2019: https://bbs.hcbbs.com/thread-2326100-1-1.html 1. For rolling bearings lubricated with grease, the higher the rotational speed, the (less) grease should be used. 2. For rolling bearings lubricated with oil, the higher the rotational speed, the (unchanged) oil level should remain. Wednesday, March 6, 2019: https://bbs.hcbbs.com/thread-2341380-1-1.html Briefly describe the conditions under high-pressure (high inlet pressure) operation; what considerations should be taken into account when selecting a centrifugal pump? Answer: 1. Pressure resistance of the casing: The wall thickness of the casing should be sufficient; reinforcement ribs should be used at areas prone to deformation, such as large flat surfaces under high pressure, and the flange grade and type must meet the requirements of the operating pressure ； 2. Bolt strength: Verify whether the tensile strength of the bolts connecting the pressure-bearing shells meets the requirements ； 3. Static sealing points: Verify the pressure-bearing capacity of gaskets and seals – considering their type, structure, material, and dimensions; for seals at joints, plug connections, and similar locations that are subject to pressure, reliable structures and dimensions should be used ； 4. Mechanical seal: A suitable sealing structure is adopted (such as balanced type, double-end face type, etc.) ； 5. Axial force balance: High inlet pressures can cause additional axial forces, leading to rotor displacement or friction between moving and stationary components; measures should be taken to counteract or accommodate this axial force (by appropriately increasing the bearing specifications to enhance their load-bearing capacity) ； Thursday (2019.3.7) https://bbs.hcbbs.com/thread-2342425-1-1.html: A municipal drainage centrifugal pump used in a coastal area is used to draw water from a tank at a certain depth. The tank is 4 meters deep, with the suction pipe extending 2.6 meters into the tank; the pump’s inlet is designed for horizontal suction, and the vertical distance from the center of the suction inlet to the water surface is 3.5 meters. The water temperature is at normal levels. The pump’s NPSHR is 4.5 meters, and the loss in the suction pipeline at its rated flow rate is 0.3 meters. Will this pump be able to operate properly once it is started after being filled with water? Why? Answer: It can operate normally. Under standard atmospheric pressure, the value of water column height – NPSHR – suction pipe losses – safety margin > vertical lift distance: 10.3 – 4.5 – 0.3 – 0.5 = 5 > 3.5. Friday (2019.3.8): https://bbs.hcbbs.com/thread-2343734-1-1.html. The operating conditions for this device are as follows: the medium is LPG (liquefied petroleum gas); at the rated flow rate, the pressure at the pump inlet is 0.94 MPa (G), and the device operates in reverse flow mode. The operating temperature is 25 degrees Celsius, at which the vaporization pressure of LPG is also 0.94 MPa (A). A centrifugal pump with a net positive suction head of 3.4 m. Without considering the effects of temperature changes and pipeline losses, is this pump operating properly? Please provide the calculation process. Answer: It can be used normally. The NPSHA of the device is equal to inlet pressure (relative) + atmospheric pressure (absolute) – vaporization pressure (absolute); this value must be greater than the pump’s NPSHR plus a safety margin of 0.6. In this case, 0.94 + 0.1 – 0.94 = 0.1 (approximately 10 meters of water column), and 10 > 3.4 + 0.6 = 4. Saturday, March 9, 2019: https://bbs.hcbbs.com/thread-2344653-1-1.html 1. The inner diameter of the pipeline is 250 mm (10 inches); with a volumetric flow rate of 420 m³/h, the average flow velocity in the pipeline is 2.38 m/s. 2. The diameter at the contact surface of the mechanical seal is 80 mm, and the pump’s rotation speed is 2900 RPM; thus, the linear velocity at that contact surface is 12.15 m/s. Have a great weekend!