Tartan 27' owner
Join Date: Jan 2008
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I am sorry to have poo-pooed your idea. It seems as though Bene505 might be the best person to try your idea out with. A simple prototype could be made from a flat sheet of thin rubber or even FRP. It is an interesting idea that would appeal to boat owners who have chronic problems with waste water back flow into the head. Of course, those using porta potties would have no use for such an invention.
IIRC your boat's 4 heads each are connected to bladder type holding tanks. IIRC these bladder tanks are mounted higher then the actual heads themselves. I am reasonably sure that your tanks have at least one air vent in them (some have none, which is a recipe for a pretty chitty mess). This plumbing arrangement creates the perfect set up for back flow from the tank to occur, IMHO.
That 'flappy rubber part at the bottom' (aka, joker valve) is designed to allow waste to be pushed through in one direction when pressure from your pump pushes it. It is NOT designed to stop all liquids from percolating back into the head mechanism if there is any back pressure (eg., gravity, heeling of the boat etc).
Perhaps the run of waste pipe to the tanks does not go up high enough to prevent waste from running back down to the joker valve where it will seep back into the head. If the tanks are mounted just below your deck level there will not be enough room to create a high point in the run to prevent back flow.
I just re-read a section of Peggie Hall's book where she discusses bladder holding tanks. She does not have kind words to say about this arrangement especially when it comes to controlling odors. It sounds to me as though you might benefit from David's idea since it may help treat the symptom but not the cause of your head problems.
I have installed a Groco head re-build kit and it is not difficult to do and not as nasty a job as it might seem IF the tank has been pumped out first. I have been meaning to get the rebuild kit for the head on my own boat as well. Some of the re-build kits are kind of pricey for the small amount of parts you actually get. A boat owner I know (Bene 1st 51') told me that he just gets a new manual Jabsco head when problems start arising with the 'older' units instead of trying to fix them. If the service kit costs $50 and a new head costs around $200 then if you install a brand new complete head you may have spent $150 more but everything is brand spanking new for nearly the same amount of time and effort.
A new head will likely pump with more pressure but will not necessarily stop the back flow from your tanks if the plumbing was not done properly in the first place though. Beneteau chose to use the bladder tanks on your boat for the obvious reason that they fit well tucked away behind the liners. You might want to speak to Beneteau to find out how they have handled this problem with other boats like yours.
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