A Few Things About Pump Piping System - Online Article

There should be at least 10 diameters of pipe between the suction of the pump and the first elbow. This is especially critical in double-ended pump designs as the turbulent inlet flow can cause shaft thrusting, and subsequent bearing problems. If an elbow must be installed be sure it is in a plane at right angles to the pump shaft to prevent an uneven flow to both sides of a double suction impeller.

  • Pipe from the pump suction flange to the pipe rack, not the other way around.
  • Make sure eccentric reducers are not installed upside down at the pump suction. The top of the reducer should go straight into the suction flange.
  • Piping should be arranged with as few bends as possible. If bends are necessary use a long radius whenever possible
  • If an expansion joint is installed in the piping between the pump and the nearest point of anchor in the piping, It should be noted that a force equal to the area of the expansion joint (which could be a lot larger than the normal piping size) times the pressure in the piping will be transmitted to the pump proper. Pipe couplings that do not provide an axially rigid connection have the same affect. If an expansion join or non-rigid coupling must be used, it is recommended that a pipe anchor be installed between it and the pump.
  • Be aware that radial forces are being generated in the pump housing from the pressure in the piping system acting on the volute area. The magnitude and direction of the forces is dependent upon the piping arrangement along with the areas and pressures involved.
  • It is always a good idea to increase the size of the suction and discharge pipes at the pump nozzle in order to decrease the head loss from pipe friction.
  • Suction piping should be at least one size larger than the suction flange at the pump.
  • If increasers are used on the discharge side to increase the size of discharge piping, they should be installed between the check valve and the pump.
  • Both a check and gate valve should be installed in the discharge piping with the check valve placed between the pump and the stop valve to protect the pump from reverse flow and excessive back pressure. Manually operated discharge valves that are hard to reach should have some facility for quick closing. A sprocket rim wheel and chain or a remotely operated motor are two alternatives you might consider.
  • Suction piping must be kept free of air leaks.
  • The installation of check valves should be avoided in the suction piping although they are often used to reduce the number of valves that have to be operated in switching between series and parallel pump operation.
  • A foot valve is often installed in the suction piping to aid priming. Do not install them if the pump is operating against a high static head because failure of the driver would allow liquid to rush back suddenly causing water hammer. This is especially true for vertical turbine and submersible pumps that are not designed for use with a foot valve.
  • Foot valves should be of the low loss flap type rather than the multiple spring variety and have a clear passage for the liquid at least the same area as the suction piping.
  • A horizontal suction line should have a gradual rise or slope to the pump suction.
  • Cast iron pumps should never be provided with raised face flanges. If steel suction or discharge piping is used, the pipe flanges should be of the flat face type and not the raised face type. Full-faced gaskets must be used with cast iron flanges.
  • The optimum control valve location is within five feet (1,5 meters) of the pump discharge to prevent too much surging of fluid in the system when the discharge is throttled.
  • The optimum pipe size will consider the installed cost of the pipe (the cost increases with size) and the pump power requirements (the power required increases with pipe friction)
    • Try to limit the friction loss at design flow to 2-5 feet for each 100 feet (1-2 meters for each 30 meters) of pipe).
    • To prevent the settling of solids you need a minimum velocity of about 4 to 7 feet per second (1.5 to 2.5 meters per second)
    • Velocities of no more than 10 feet (3 meters) per second are recommended in the suction side piping to prevent abrasive wear.

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