Centrifugal Pump: The Important point you must Know

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centrifugal pump
  • The current will increase to a very high value if the discharge valve of a centrifugal pump is completely shut off.
  • Cavitation erosion occurs due to physical action.
  • After overhauling a centrifugal pump you have found that the motor electrical connection was wrongly done and the pump is rotating in the opposite direction. Both the pump discharge head and the capacity will be affected.
  • Centrifugal pump liquid filled inside casing prior to starting for priming.
  • The lantern ring in the centrifugal pump is located between gland packing.
  • A submerged type centrifugal pump is sometimes used as the main L.O. pump as the flow rate required for main L.O. systems is very high.
  • The emergency fire pump is fitted with a ¬†fixed vane-type priming vacuum pump and needs to be filled with sealing water in the tank. If after some days after trials, the water evaporates or the tank gets empty, the fire pump may not take suction as even after the vacuum pump gets engaged, and may not develop a vacuum in the suction side, .due to sealing the water tank is empty.
  • The centrifugal pump is not provided with a safety valve while a positive displacement pump is provided, because the centrifugal pump is so designed that it can withstand high pressure.
  • Net Positive Suction Head (NPSH) is the difference between Static suction head and the vapour pressure of the liquid. NPSH and the Total suction head are two terms that are commonly used for pumps. The total suction head is greater than NPSH. Throttling the discharge valve of a centrifugal pump the NPSHr, decreases.
  • Double-entry impellers have a distinct advantage over single-entry impeller, as it gives a higher pumping efficiency.
  • A grease-lubricated ball bearing or roller bearing will run cooler if the grease has a high grease penetration number.
  • Removable sleeves are installed on centrifugal pump shafts, as they can be economically replaced as they wear out, instead of the full shaft.
  • An emergency fire pump has been lined up for supply to the fire hydrant on deck. As soon as the pump is started the vacuum pump engages. The suction of the pump goes into a high vacuum but the pump discharge pressure remains zero, and the vacuum pump does not disengage, The pump suction filter might be clogged, which is the most probable cause for the pump not to take suction.
  • After overhauling, a centrifugal pump and while assembling it is noted that installing the o- ring between the sleeve (provided in way of gland packing) and the shaft, is missed out, it will cause leakage of fluid(air/water) in between the shaft and the sleeve and will affect the pump performance.
  • A centrifugal pump having a double entry impeller was dismantled but forgot to do the markings while dismantling. The direction of rotation and/or the shape of the volute casing will help you to put the impeller in the correct way during installation.
  • The purpose of balancing holes on a single entry closed type impeller of a centrifugal pump is to balance out the axial thrust on the impeller and hence on the shaft.
  • Central priming system, attached vacuum pump, and seawater priming method are used for priming of centrifugal pumps onboard ships.
  • The pump-driven clutch is the drive used for the attached vacuum pump of a ballast pump.
  • While started pumping out a Fore peak tank, the ballast pump is running showing a low discharge pressure but a positive suction pressure, Chief Engineer was required to throttle the discharge valve to increase the back pressure on the pump. Centrifugal pumps cannot operate at greater than rated capacity, so throttling the discharge valve is only going to decrease the discharge rate below-rated capacity.
  • While being overhauled a centrifugal pump and while assembling, installing the o- ring between the sleeve (provided in way of gland packing) and the shaft, is missed out. It will cause leakage of fluid(air/water) in between the shaft and the sleeve and will affect the pump performance.
  • The attached vacuum pump of a ballast pump operates on the principle of a vane pump.
  • Increasing the rotational speed of a cargo pump, the pump flow rate will Increase in direct proportion to the increase in speed.
  • The correct method of greasing a centrifugal pump bearing is, to pump the grease when the pump is running and drain any old grease at the same time by opening the drain plug, until all the old grease is removed and new grease starts coming out of the drain, repeating same for each bearing. the drain plug should then be replaced.
  • The main disadvantage of a centrifugal pumps is that they are not self-priming in nature.
  • For shaft sealing of a main seawater pump for ships plying in coastal muddy waters, gland packing is the best option.

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