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Rare earth magnet for solenoid core

  1. May 6, 2009 #1

    I am trying to design a simple water valve that opens a plug in a small water reservoir until its empty.
    So far I have a solenoid coil wound around a hollow core plastic pipe with a cylindrical rare earth magnet inserted halfway into the pipe with a 'plug' attached to the top of the other half. Switch power on and the magnet pops out lifting the plug allowing water to flow around the magnet core through the pipe. Total movement of the core is restricted by a string attached to the bottom of magnet and plastic pipe. After power shut off the plug just falls back into place sealing the reservoir.

    Since everyone else seems to use a standard ferrous material for the movable core, is there actually any point in using a magnet here?

    Thanks in advance ..

    EDIT: I used the rare earth magnet in the hopes of obtaining more force for less current ..
    Last edited: May 6, 2009
  2. jcsd
  3. May 6, 2009 #2


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    Science Advisor

    If you put an soft Iron core in a solenoid, it will tend to pull inwards to the center of the solenoid when you apply power.

    Using a magnet does allow you to get movement out of the coil instead of into it, if you get the polarity right.

    That is also how you remagnetize the magnet, so starting off with a very strong magnet will make this less likely.
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