Self draining heat exchangers?

Discussion in 'Propulsion' started by sdowney717, Feb 27, 2015.

  1. sdowney717
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    sdowney717 Senior Member

    The idea is have them drain when engine turns off, for me just drain them into the bilge.

    My thinking is freeze protection and also less corrosion potential.

    What would be best would be a passive valve, say closed under pressure, but when pressure lets off low, it opens. Would a swing gate valve do that?

    Otherwise maybe a valve with a spring that the pump overcomes causing a closure, but pump stops, the springs opens the valve. Other idea is an electric valve.

    I have 4 heat exchangers.
    2 for the engine coolant
    2 for the engine-trans oils.
     
  2. gonzo
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    gonzo Senior Member

    It will lessen the freeze danger. However, you will be introducing more oxygen, which will increase corrosion.
     
  3. sdowney717
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    sdowney717 Senior Member

    I had wondered about corrosion flooded versus drained.

    I suppose the best imaginable system would be fresh water flush then drain. And automated, because I know people wont take that time to do that, including me, so then nothing gets done.

    these Sendure heat exchangers are most likely original to the boat from 1970 and it has always been ocean - bay water. When I got the boat in 1998, several of the tubes in both exchangers had leaks, which I silver brazed closed by pulling the end caps. They are good quality.

    Why do you think some of those tubes developed a leak, is it typical frost or corrosion damage? I think those tubes are a copper nickel tube.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Corrosion is the usual problem with exchangers. If they're kept boiled out and clean, usually long service life. If permitted to clog and corrode, not so much. I've saved many an exchanger with a professional boiling. The transfer tubes might be monel, but bronze is more common and a fair bit cheaper too.
     
  5. CDK
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    CDK retired engineer

    A simple float valve or non-return valve, as used in central heating and potable water systems can do the trick.
    Installed in the highest point of the cooling circuit, it allows air to enter when no pressure from the raw water pump is present, so the heat exchanger slowly releases its contents in the exhaust. If your engine and exhaust are above waterline, you've reached your goal.

    Of course you cannot do this with engines below the waterline.
     
  6. FAST FRED
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    FAST FRED Senior Member

    Your best choice to have a boat that can be operated in freezing weather , and to just walk away when docking is the standard as used by Lobster guys.

    A dry stack with keel cooling only leaves the boats FW system and toilet to worry about.
     
  7. sdowney717
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    sdowney717 Senior Member

    http://www.sprinklerwarehouse.com/The-Freeze-Drain-Irrigation-s-Best-Kept-Secret-s/7952.htm

    Maybe I need to think how they do this with automatic sprinkler systems.
    Or maybe CDK's idea. The auto vent type, might work, if put on its side below the heat exchanger. Pressure from pump closes valve, pressure goes away, valve opens?? OR would the weight of the water in the exchanger keep enough pressure on valve so it will not open, if it is just a float design, i dont think that is going to work.

    Idea is a valve that high raw water pump pressure shuts and low pressure, valve opens.

    http://www.sprinkler.com/sprinkler-...allation-manual/automatic-drain-installation/
    http://plumbing.about.com/od/irrigation/a/Automatic-Drain-Valve.htm

    Here is a product list, they are cheap.

    http://www.sprinkler.com/product-ca...em-parts/additional-system-parts/line-drains/

    Ebay also cheap, wonder if Lowes or Homedepot sells these.
    http://www.ebay.com/itm/Two-Orbit-1...996?pt=LH_DefaultDomain_0&hash=item3cf1e301fc
    Anyone have links to read?

    My Main heat exchangers have 1/2 inch pipe thread drain plugs. It would be easy enough to hook up a drain using a short piece of hose, placing valve in position to dump into the bilge.
    The two oil coolers use 1/4 inch plugs, so would need thread adapters.

    I called Lowes and HD, only Lowes sells them at $3.00 each in 1/2 inch thread. So will go and see for myself
     
  8. kapnD
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    kapnD Senior Member

    This discussion is, so far, all in the assumption that you always have raw water pressure when underway.
    If you experience a water pump failure, intake blockage, broken hose, or similar, overheating will occur in very short order with this system installed.
    Be sure to have a raw water flow alarm installed, and I would put a ball valve over whatever type of drain you use, for redundant control.
     
  9. sdowney717
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    sdowney717 Senior Member

    Ok, but I have had impeller failures which causes the engine overheats in a couple of minutes, which will cause the same as a blockage, which I have also sucked up I think Jellyfish causing impeller failure and overheating.

    Worst situation was on a strong outflowing tide, one engine fuel pump failed, so I had only one engine working coming back in, and then the impeller disintegrated in the other leaving only the core. Then we threw out the anchor, it did not hold, likely landed on its side, and so we dragged out into the Chesapeake Bay. So there i was with about 6 family people and it is super hot July day and the engine blowing steam out the heat exchanger. And I get to fix it, glad I had extra impellers. I think I will switch to globe, they can run dry and not fail versus the black ones which cant run dry except for a few seconds.
     
  10. kapnD
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    kapnD Senior Member

    Sdowney,
    I think we have all had the pleasure at one time or another!
    What I have learned is that the cost of an annual impeller change is cheap insurance against frying a motor in a moment of inattention.
    Even this will do nothing when you suck up a plastic bag or a jellyfish, so I have installed a raw water flow alarm and an overtemp switchguage, both wired to a loud bell under the console that can be heard quite well anywhere on the boat. (It has an override button for startup)
    I am looking to install a third alarm on the exhaust elbow, my thinking is that the earliest overheat warning available would be at that point.
    I live and boat in the tropics, so the draining of the heat-x-changer is not an issue for me, but I do fresh water flush religiously.
    How low does the ambient temp get in the engine room?
    There are various kinds of heaters that can keep the engine warm in very cold weather, or a small raw water circulation pump to keep the heat x from freezing up.
     
  11. FAST FRED
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    FAST FRED Senior Member

    The heat exchanger is not all that can freeze, The wet exhaust manifold is also at risk.

    Even the sea water inlet can freeze to the point of cracking the sea cock, or any hose attached to it.
     
  12. gonzo
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    gonzo Senior Member

    In cold weather, a keel cooler is the safest option. However, running a dry exhaust may be hard to do in some boats.
     
  13. sdowney717
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    sdowney717 Senior Member

    With the recent unusual cold air down to single digits a few nights, everything in the boat will freeze that can freeze
    My manifolds AND risers are all FWC, so are antifreeze protected. I modified the risers by brazing on a bronze pipe niple to the end, closing off the original water exit and welding in a SS tube so that sea water flows only in the added extension.
    After spending $1000 on risers, I never wanted to replace them again, been good now since 1998.:p

    This year I did suck up some red antifreeze into the head and Lectrasan and put a light bulb in there, glad I did.

    Boat has about 2 inches of frozen sea ice in the bilge. The front bilge is more salty and the rear bilge is mostly rain water. By wednesday, it will be mid 60's so when I go out there, should be thawed out, I think!

    As far as temp warning on failed flow, I have been thinking dryer thermostats, they are NC and thinking of getting one that opens about 230*F to open circuit the engine ignition. I would need 4 of them mounted for each exhaust bank. That way and overheating engine would kill the motor, likely quicker than I can notice.

    They can be hose clamped on. I was thinking either clamp onto hose or cut a small hole in the hose or clamp onto bronze riser extension. Likely direct metal contact would be best. You cant overtighten them or you will deform the surface of the thermostat, if you were clamping against an unyielding metal part..
     
  14. kapnD
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    kapnD Senior Member

    I am shy of shutdown thermostats.
    What if you are running the inlet on a nasty day and the engines start overheating?
    I would sacrifice an engine to save the boat. (not to mention my ***!)
    Murphy dictates that the worst possible things will happen at the most inopportune moments.
     

  15. sdowney717
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    sdowney717 Senior Member

    You could make it work fancier.
    You could have it sound a warning which if you do not override within x number of seconds with a switch, it shuts down the ignition circuit.

    There is a risk of actually setting fire to the exhaust hoses with no cooling water flow.
     
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