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Sea Water Overboard Valve Shorting to Hull

Discussion in 'Technical Discussion' started by Globetrotter76, Jul 1, 2010.

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  1. Globetrotter76

    Globetrotter76 New Member

    Joined:
    Oct 20, 2004
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    Location:
    Cape Town - South Africa
    I am about to start troubleshooting a problem onboard.

    I have only been onboard for one month and have been informed that the sea water overboard valves have been replaced in the last yard period and were tested for continuity and they were all okay, however at the end they re checked and one is showing a short from the Valve to the Hull which is Aluminium.

    Any ideas or suggestions as to this issue and ideas troubleshoot, I hope to take a poke around 2 morrow.

    Any thoughts and comments on this topic would be great as we can share information and educate further

    Thanks

    Globe
  2. K1W1

    K1W1 Senior Member

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    Hi,

    How is the Valve attached to the hull?
  3. Marmot

    Marmot Senior Member

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    If you are saying that the skin valves on this boat are flange mounted to welded aluminum through hull fittings and are normally isolated by way of insulating sleeves and washers on the flange bolts then there is only one answer, one or more of the sleeves or washers has failed or been removed or some other item is forming a circuit between the valve and the fitting.

    What is on the upstream side of the overboard valve in question? Is it rubber hose or a rubber isolator? Is it metallic pipe? What is that pipe connnected to and how? If so has that been changed and does either one incorporate a grounding conductor?

    Are you the engineer? Have you ever worked on this type of system before? If you expect complete electrical isolation of systems from skin valves and hull your future is going to be a disappointing one. It doesn't take much corrosion or the addition or modification of any part of the system to instantly make everything electrically common. There is a valid argument to be made that it should be anyway. Usually it all falls apart the first time someone can't find an insulating sleeve or washer and just says, "screw it, I'll get to it later."
  4. Globetrotter76

    Globetrotter76 New Member

    Joined:
    Oct 20, 2004
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    Location:
    Cape Town - South Africa
    Hi Folks

    Thanks for comments Marmot, I will get to a few of your questions as I got side tracked with another problem by being woken up by an alarm at 2am this morning, thats another topic all together(AC Earth Faults)

    Yes I am the Engineer onboard. I have never worked with this kind of system before. At this point I have just glanced at the valve as I have been handed over a work list so I am trying to educate myself on a topic that I am not overly some knowledge and basic not much experience on.

    From your description Marmot from my brief glance at the valve which is tucked away and obscure it looks like it is welded to the hull and are flange mounted. Do you have link to pictures or tech drawings of this kind of setup?

    So I am looking at the presence or non presence of insulating sleeves and washers? Upstream of the valve it seems like it is stainless steel pipework(Not sure of which grade) Not sure about your other questions at this time.

    I am trying to educate myself on topic before I start my own troubleshooting.

    Thanks

    Globe76
  5. Marmot

    Marmot Senior Member

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    Here are a couple of pictures of the sleeve system.

    Attached Files:

  6. Globetrotter76

    Globetrotter76 New Member

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    Location:
    Cape Town - South Africa
    Thanks Marmot, I am still troubleshooting another AC Earth Fault onboard, so this is on the backburner for now.