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  1. #1

    hot water system expansion tank

    I traced a wet bilge area to overflow from the hot water tank pop-off valve. It seems that each cycle from cold to fully heated produces about 1/2 pint. This occurs from either AC power or engine water loop. So, one could pipe this directly overboard or into a nearby sump to keep the bilge dry. But I am wondering why boats do not have an expansion tank above the hot water tank? All newish houses and condos in my part of the country have them. Must be a code requirement.
    Reading Calder, WM and other catalogs I find the typical schematics showing an accumulator on the cold water side but never an expansion tank for hot water. The only reference I have found for expansion tanks on a boat is in hot water heating systems such as Webasto.
    The one in my house is only as large as a typical "marine" accumulator tank. Why not pick one up at home despot for cheap and put it on the boat? I'm thinking it will also keep the psi from getting too high when a tap is not opened for several hours.
    comments?
    Gary

  2. #2

    Re: hot water system expansion tank

    Is there an accumulator in your fresh water system at all? It doesn't matter where you put it as long as it is "connected" to the hot water heater somehow and not behind any check valves.

    I believe the new code requirement is to prevent pressure from rising too much in the house (because of the hot water heater) and overpowering the "backflow preventer" (check valve) in the main water supply.

    However, a house system has a lot more volume, so such rise in pressure due to heating normally isn't a problem....and you usually keep the hot water heater on constantly.

    In a boat, the volume of your system is much smaller so a small expansion of water due to increase in temp will cause a greater increase in pressure.

  3. #3

    Re: hot water system expansion tank

    Krush is right, but I think I would change out the pop-off valve. The system should not be running that close to the pop-off pressure. Sounds like a tired pop-off or you have a really, really small system. I have no accumulator and I have never trigger the pop-off. My water temp runs from a cold 35 to 180 degrees hot. Your system also will include your cold also because they both are fed from the same source. Once the system is charged the check valve won't do a whole lot unless there spring loaded and most are not. There to prevent back flow of hot water. Since they are a gravity type check they will weep a little and equalize the preasure when there is no flow. At least mine is.
    BILL
    Last edited by Trojan; 02-08-2008 at 01:20 PM.

  4. #4

    Re: hot water system expansion tank

    The over pressure/temperature valve in my boat is plumbed overboard and not into the bilge. My valve went bad one time and I noticed water coming out of the fitting. I thought all Hatts were plumbed this way. Sounds like you need a new valve. Ron

  5. #5

    Re: hot water system expansion tank

    Bill is right too (this can't be happening LOL). You may need to replace the valve.

    If you are blowing the pop-off valve, you are putting a lot of stress on other parts of the system (if it is working correctly). I think the pop-off valve is around 120psi.

    Here's what happens when they go out of control heating: it's bascailly a boiler explosion! http://www.safteng.net/Accident%20Ph...0explosion.htm




    This guy sums up the system and components for ya. It will help you solve the problem: http://www.factsfacts.com/MyHomeRepa...sureRelief.htm

  6. #6

    Re: hot water system expansion tank

    Quote Originally Posted by Beckytek View Post
    The over pressure/temperature valve in my boat is plumbed overboard and not into the bilge. My valve went bad one time and I noticed water coming out of the fitting. I thought all Hatts were plumbed this way. Sounds like you need a new valve. Ron
    Mine is plumbed that way and I had no idea why I was loosing pressure when turned the pump off and was away from the boat. Then when on the hard, I saw a slight trickle running out of the stbd sea chest thru hull. It was such a slow leak that I never would have caught it when it was in the water.
    Sky Cheney
    1985 53EDMY, Hull #CN759, "Rebecca"
    ELYC on White Lake--Montague, MI

  7. #7

    Re: hot water system expansion tank

    Good inputs, thanks all.
    Yes, the 31 EC is a small system. Just galley and head with the shower being a handheld quick-disconnect to the head sink. There is no accumulator tank and this is consistant with my Hatteras schematic. There are indications that I am building up a lot of pressure. I have been chasing drips in all hose connections on the hot water side. This tells me that I do not want the pop-off operating at a higher pressure.
    I had not considered that an accumulator on the cold water side could address this as well as the intended purpose of reducing pump cycling. I gotta think about it now; will probably lose some sleep tonite!
    Gary

  8. #8

    Re: hot water system expansion tank

    Try turning the temp down 10 degrees unless you really need scalding water.
    If the lines are leaking at connections, you dont need more pressure. Thats a good reason to disconnect the shore water WHENEVER you leave the boat.
    I kill mine even when we go to breakfast... Ya never know, you might get that call from home, or these days get arrested for a parking ticket and have to leave the boat un-attended for longer than you thought. ws
    yachtsmanWILLY

    I used to think I knew everything until I found the experts HERE; Now I know I dont know SQUAT



    www.flybridge.proboards.com
    Uncensored, no nonsense boating fun for adults

  9. #9

    Re: hot water system expansion tank

    Bill is absolutely right,always shut off the dockside water or at least install one of those garden type gallon/timers. I once helped a fellow dockmate save his 66' Chris Craft that was sinking at the dock due to a broken freshwater line. His 12volt charger that maintained the battery that ran the bilge pumps had unknowingly quit and so did the pumps after a while.

  10. #10

    Re: hot water system expansion tank

    The battery charger probably quit when it was below the flood water level!

    Our later 36 has an overboard discharge for the hot water relief valve, an accumulater, and a preassure reducing valve. Because both hot and cold water are completely connected to each other, what affects one affects the other. Maybe his smaller Hat doesn't have that preassure reducing valve. That thing drives us crazy. Ours hums a tune whenever a faucet is turned on when shore water is being used. I can't believe that a little 6 gallon tank can create enough expansion to be a problem. An accumulator will surely help and it will make water operation much smoother when using the onboard pump. I would surely install one. He probably does not have the peassure reducing device either. I will bet his marinas water supply preassure is way high.
    The small marine type tanks do not have a temperature selector, so that won't help. We have popped our overtemp switch on the tank because I have plumbed the anti-freeze loop to one of our engines. On a long run, the water in that tank gets hotter, (from the coolant loop), than the limit switch will allow. Having hot water available while underway is very nice though.
    Maynard
    UNITY '86 36C

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