Pump Handbook

Positive Displacement Magnetically Coupled Pumps (Cont.)

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B - Suction Piping

    Design the suction piping to reduce the possibility of cavitation problems.

    Generally, the suction piping should be one or more pipe sizes larger than the pump's suction connection.

    Keep the suction piping as short as possible.

    Keep the suction piping as straight as possible.

    Keep a minimum of 5 to 10 pipe diameters of straight run in the piping prior to the pump inlet.

    Avoid high points in the suction piping. Go around objects instead of over them.

    Reducers used in the suction piping should be eccentric with the flat side to the top.

    Strainers should be used to prevent foreign objects from entering the pump. The strainer should be sized based on minimum pressure drop and not on line size.

    Valves in the suction line should be sized for minimum pressure drop, and never used as throttling valves.

    Always provide a gauge connection between the suction valve and the pump connection. The gauge connection should be located as near the pump suction connection as possible.

    Insure that the suction piping connection to the source reservoir is sufficiently submerged or baffled to prevent vortices or drawing in air.

    Don't be mistaken in believing that a flooded suction will always provide sufficient NPSHa. Calculate the losses in the suction line to insure you have sufficient NPSH available.

    Support the piping independently of the pump. (A pump is a very expensive pipe support.)

    Use expansion loops or flexible connectors in systems where thermal expansion of the piping will occur.

C - Discharge Piping

    Support the piping independently of the pump. The piping should line up naturally with the pump connection and not need to be forced into position.

    Provide a discharge valve for isolation of the pump should maintenance be required.

    Provide a discharge check valve located between the pump discharge connection and the discharge isolation valve.

    Provide a pressure gauge or gauge connection on the discharge as close to the pump discharge connection as possible and before any valves.

D - Safety Devices

    Magnetically coupled positive displacement pumps can experience some unique problems if not properly operated. One or more of the following devices should be considered when installing a magnetically coupled positive displacement pump:

    • Flow Switch: This would be used to prevent operating the pump dry.

    • Pressure Switch: This could be used to shut the pump down on high or low discharge pressure. This could be used to prevent dry running or to prevent the de-coupling of the drive magnets due to excessive discharge pressure.

    • High or Low Amp Relay: These could be used to shut the pump down on high or low amp draw by the motor indicating high discharge pressure or in the case of low power draw, running dry.

    • Power Monitor: A Power monitor would be used for the same purpose as a high and low amp relay, but provide a more accurate control of the set point, providing less opportunity for false trips.

    • Temperature Switch: Most magnetically coupled pumps have provisions for connection of a temperature switch or temperature sensor at the magnetic coupling. This temperature switch/sensor should be used to shut the unit down or activate an alarm if the temperature exceeds a predetermined point above the normal operating point of the pump. The magnets used in magnetically coupled pumps are generally a rare earth type that will be permanently damaged or destroyed if the magnet's temperature limit is exceeded.

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