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Vacuum toilet issues

Discussion in 'Technical Discussion' started by Jw-marine, Sep 28, 2015.

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  1. Jw-marine, Sep 28, 2015
    #1
    Jw-marine

    Jw-marine New Member

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    Hello everyone been having problems with a vacuum toilet system on a boat I've just joined.

    The motors we are using are single phase induction motors coupled to a vane pump.

    Both seem to take a long time to create the vacuum required to reach the set point for them to cut out.

    One pump gets hot and takes a lot longer than the other to reach the set point.

    I went to inspect the system today and the whole vacuum system is very hot.

    There is a small tank separate from the main black tank and this is full of water. I don't really know the function of this tank?

    This tank has the vacuum pipe from the main black tank going into it and out of it a breather down to a skin fitting, then a fresh water feed in and a feed out to the pumps which create the vacuum which I'm assuming is to keep water circulating through the pump to cool them? Or keep them primed?

    It's the first time I've worked on a boat with a vacuum system and I'm struggling for ideas now. We had all the pipe work re made and looks like a good job seems air tight.

    I will strip the pumps tomorrow and inspect them but apart from that does anyone have any ideas?

    Boss arrives soon and I need the system sorted, it runs as it is but both pumps are getting hot and taking much longer to create vacuum set point than what it should.

    Thanks in advance.
  2. K1W1, Sep 28, 2015
    #2
    K1W1

    K1W1 Senior Member

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    Can you share with the group what brand of system it is?

    Have you checked that the fittings and holes in the pipes that the switches are connected to are all clear and free?

    This is not uncommon and there are plenty of guys who have done days of work dismantling and re assembling pumps and stuff only to find it was something very simple.
  3. Jw-marine, Sep 28, 2015
    #3
    Jw-marine

    Jw-marine New Member

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    Hello KIWI,

    There is no branding anywhere, the best I can do is upload some pictures of what I have.

    Tomorrow I will start to strip the pumps as one has a slow leak from the pump housing.

    Can anyone explain the function of this second tank I mentioned in my first post? I've searched vacuum toilet technical drawings but none of them seem to have this second tank!

    Thanks again.
  4. K1W1, Sep 28, 2015
    #4
    K1W1

    K1W1 Senior Member

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    Are they controlled by separate switches? If so change the cables around so the pumps use each others switch, this will quickly eliminate a common problem.

    If posting photos please remember to keep them to the required size.

    I will have a look and see if I or one of my colleagues can work out the system if your photos are clear of all parts you are asking about.
  5. Jw-marine, Sep 28, 2015
    #5
    Jw-marine

    Jw-marine New Member

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    Okay so I forgot to mention I have put pump no1 electrical supply into pump no2 as when I first joined the boat pump no2 wouldn't run, I took capacitance readings from start and run capacitors these were ok. Turned out the impeller was seized from not being run for a while.

    After freeing up the pump it ran fine on either supply.

    The pumps are both controlled by Plc and off the same switch. The pumps cannot run at the same time they can only be swapped from one to the other.

    Will do my best for pictures tomorrow.

    Thanks again.