pumps: Questions related to pumps

  • What is NPSH?
  • Ans : It is measure of the pressure drop of the liquid as it moves form the inlet of the pump to the eye of the impeller, determined by testing and expressed in feet of water by pump manufacturer.
  • What is cavitation?
  • Ans : Cavitations is a rapid collapse of vapour pressure that can produce noise, result in loss of head and capacity and create a severe erosion of the impeller and casing surface in the adjacent inlet areas.
  • What is velocity head?
  • Ans : The head loss caused by the consumed power to accelerate stationary fluid to suction line velocity during pump start-up. It’s about 1 ft.
  • What is standard for petroleum pumps?
  • Ans : API 610 is the standard for centrifugal pumps in petroleum industry.
  • Where positive displacement pumps are used?
  • Ans : Used to move viscous liquids, injects chemicals or additives into a system, or pump quantities too small for centrifugal pumps.
  • What are types of rotary pumps?
  • Ans : External Gear, Cam and piston, two lobe, three lobe, single screw, Two screw.
  • Where rotary pumps are used?
  • Ans : For viscous liquids that are free of hard and abrasive fluids.
  • Where should boiler feed water pumps be located?
  • Ans : They take water from a deaerator and generally operate close to the vapour pressure of the liquid, hence they must be located as close to the deaerator as possible.
  • Tell something about vertical pumps?
  • Ans : Used where low available NPSH is not sufficient, for surface condenser, for waste material in concrete pit, screen at the bottom.
  • Where centrifugal pumps in vacuum service are located?
  • Ans : directly below tower, may be on spring supports.
  • How to support discharge line of centrifugal pump?
  • Ans : Discharge line should be supported as close to the top elbow as possible and should be within five diameters of that elbow, using spring support.
  • How suction line is supported?
  • Ans : Commonly supported under the elbow adjacent to the pump nozzle.
  • How the suction line reducer should be placed?
  • Ans : It should be placed top flat.
  • What are suction line requirements?
  • Ans : To flat reducer, strainer, block valve, no pockets, as short as possible with consideration to stress, min straight length of 3D.



  • What are the requirements of discharge piping?
  • Ans : Reducer, Pressure indicator, check valve, block valve, min. stress, support at top elbow.
  • What is accepted distance between pumps? 
  • Ans : 1200 MM / 4 feet.
  • What is special requirement for discharge line of positive displacement pump?
  • Ans : Relief valve whose discharge is connected in suction line between the isolating valve and the pump.

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