Eruptive heads - all heads together

[sundance]

HELP!

On our one-year old Hunter (Legend) 326 we have a serious problem with the heads. It goes something like this. When using the system to pump solid waste, the first sign of all not being well occurs after about five pump strokes when nothing further happens; the sytem kinda comes to standstill in a "no man's land" with a half full bowl determined to stay that way as the unfortunate occupant struggles with equal determination to get rid of it. But, any attempt to persist in further pumping is inviting serious trouble in the form of a volcanic type eruption in the bowl - with all sorts of unpleasant consequences. It does not happen at all when dealing with urine discharge and it is at its worst when the system is on the holding tank setting.

The manufacturers technical representative has been to the boat to try and rectify the situation and finding "nothing obviously wrong" decided to change the loo, and its associated piping etc., to be on the "safe side"! Alas, his labours came to nothing. There is no change - in fact, if anything, it seems to have got worse!

Please help, all you head mistresses and masters- my blushing bride of not many years, a private sort by all accounts, particularly private when it comes to her ablutions, is finding Med cruising on our new boat less romantic than her dreams. Yes, her dreams are more than a little shattered....................... and I see a strange longing look to landward in her eyes as she emerges from embarrassingly lengthy soujourns to the head!


James


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[cliff]

Had experience of the "exploding bog" syndrom. Caused by back pressure in the discharge line or holding tank overcoming the aortic valve after much pumping and blow back as the aortic valve reverses itself.

Piddle can sometimes leak past the valve or blockage but not solid waste.

Check the holding tank is vented and the vent is clear.
Check the valve between the holding tank and the bog is open (if a valve is fitted)
Open the pump and check the aortic valve is not reversed and is seated properly.
Check discharge pipe from teh bog to the holding tank or sea valve is not blocked. The bigger the blowback the more volume of compressed air is envolved and hence would give an indication of where the blockage is.

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[cliff]

Might also help if your bio gave a bit more info like where you are based

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[HeadMistress]

I don't think the toilet is the problem...I strongly suspect a blocked holding tank vent.

An empty holding tank is full of air...as the tank fills, a volume of air equal to the volume of each flush must escape out the vent or the tank becomes pressurized, creating increasing backpressure that prevents anything more from going into the tank. Since no air--or considerably less than has to--in the tank can go out the vent, it's gonna escape anywhere it can...and that would be via the hose from the toilet...you push while pumping...it pushes back until "Thar she blows!" If it can't get out through the toilet, it may blow a fitting off the tank and can even crack the tank...which is why you should NEVER continue pumping a toilet against increasing backpressure. Nor should you attempt to pump out a tank until the vent has been cleared. The pumpout won't be able to empty the tank...it will only pull a vacuum that can result in a cracked tank.

The most common locations for a blockage in the tank vent are the vent thru-hull and the connection on the tank. Mud daubers love to build their nests in thru-hulls, dust and pollen can clog them...and so can spilling the tank out the vent while heeled or by overfilling it. Heeling can also cause waste to flow into the tank vent line, clogging it at the connection to the tank.

If a blocked tank vent isn't the problem--if it also happens when flushing directly overboard--you may have a defective y-valve...it's not completely opening either side. Urine would have little trouble passing through a side that's only partly open, but solids would create a blockage that would create the backpressure that results in an eruption. A defective y-valve is far more likely if the valve is a Jabsco, because unlike Whale, Henderson and other y-valves which have a "barrel" inside that's rotated by the handle, Jabsco y-valves have only a very flimsy piece that moves to block one side or other other that can easily break off or get hung up.

Since the toilet and all the hoses have been replaced, there's only one other possibility: Quick-dissolve toilet paper won't create a clog that has to be cleaned out...but too much of it at one time can create a temporary clog that could be the cause of your problems...and if it happens more often to your bride than to you, it's good possibility because women seem genetically programmed to use half a roll at a time. However, unless you're using the wrong kind of TP--premium brands that advertise their strength--the clog will "melt" on its own in a very short time, relieving the pressure and allowing the toilet to be flushed again. If that is the case, and if your toilet is a Jabsco that has a 1" discharge (the only mfr who uses 1") instead of the usual 1.5", replacing it with with 1.5" discharge fitting and head discharge hose should help considerably.



<hr width=100% size=1>Peggie Hall
Specializing in marine sanitation since 1987

 

[sundance]

Very informative; many thanks.

Based on what you say would I be correct in assuming that if I remove the tank deck pump-out cap for a day or two I can do a test on the system and prove, one way or another, that a build-up of compressed air in the tank is indeed the culprit.............for with the deck cap off, such an air build-up could not happen??????

james

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[HeadMistress]

That wouldn't accomplish any more than just loosening the deck fitting cap immediately upon starting to experience backpressure when the toilet is flushed. If the tank has pressurized, you'll hear a hiss of air escaping as the toilet is being pumped....if it hasn't, you won't.

But even that won't accomplish any more than spending 10 minutes with a screwdriver in your hand scraping out the vent thru-hull...if it's clogged, you'll get the clog out, the problem will be solved. If it's not, you need to look elsewhere. Spending a day or two with the cap off does nothing to cure the problem...and won't help you identify any other cause. You'll just waste a day or two trying (I suspect) to avoid getting your hands dirty.

Besides, you need to become accustomed to doing things like checking vent thru-hulls and flushing them out regularly as PREVENTIVE maintenance instead of only curing problems. That not only applies to your sanitation system, but everything on your boat. Prevention always easier and usually a lot less expensive than cure.

<hr width=100% size=1>Peggie Hall
Specializing in marine sanitation since 1987