Y valves

[southchinasea]

I understood a Y valve fitted to the heads plumbing would enable:-

1. Discharge waste into holding tank
2. Discharge waste direct overboard (via a through hull outlet)
3. Discharging OF the holding tank when at sea. (I assume this is
via a vacum created by the water aross hull fitting when making way rather than
gravity?)

I KNEW 1 and 2 occured, but my pal seems to able to accomplish 3 on his boat (Oyster). The yard building my new boat don't seem to know what I am talking about.

Am I talking complete nonsense?
Cheers

 

[chrisc]

normal thing is to fit a discharge pump

 

[ccscott49]

The normal Y valve you are talking about, never allows the tank and skin fitting to be open at the same time, so it wouldn't work, however I have seen a system without pump, which worked on the depression over another skin fitting, but the normal way is a discharge pump to seperate skin fitting. The same skin fitting can be used, but requires an additional valve.

 

[Peter_the_Grate]

Invest in the latest copy of PBO - it is all explained there.

 

[vyv_cox]

There is a very comprehensive treatment of this topic in the West Marine catalogue. Every option seems to be explored. Look at it online at http://www.westmarine.com/webapp/co...isor.d2w/show_advisor?fn=436.htm&store_num=11 From memory this might be an abridged version but it still looks quite comprehensive.

 

[Sinbad1]

Specifics. The Y valve is fitted to the outlet pipe from the loo and allows the alternative of discharging direct to the sea, or direct to the holding tank.

Now, if you were to put a Y branch as opposed to a Y valve, in the outlet pipe, downstream of the Y valve, then theoretically you should get a venturi effect and the goods could be sucked out by this vacuum when underway. However this would require quite a large outlet pipe from your holding tank and worst of all, it would have to be taken from the bottom of your holding tank as the vaccuum would be insufficient to lift it up a discharge pipe which enters the top of the tank. As tanks tend to corrode or leak from their outlet/inlet spigot, I wouldn't like to take the chance.

To discharge at sea you need a pump. This can either be a macerator type pump (12v) or a hand operated discharge pump. The easiest way to install this is to place a Y branch downstream of the Y valve in the outlet pipe and plumb the pump into the tank outlet and from the pump to the Y branch. This way you are not creating further holes in the boat and the effect of having the Y valve discharging into the tank effectively closes the discharge pipe from the heads and makes it the discharge pipe from the tank.

Clear as mud i 'spose, but it works and is quite simple without taking up room.

The Y junction/ branch I purchased from Lee Sanitation. This was a little tricky due to the fact that the standard 12v macerator pump has a different sized outlet pipe to its inlet pipe. Got there in the end.

 

[HaraldS]

Just to make sure you don't choose this option, let me explain another one that is not working. My yard, otherwise brilliant thought it was the greatest invention since sliced bread, and I didn't protest since it was simple, in the end I had to change it though.

First idea is to always pump the toilet into the tank. Second is to put the tank up high right under the deck and then have the usual suction pipe to the deck and a relatively big pipe straight down to the seacock. (1 3/4'). This is supposed to drain by gravity, possibly a bit of ventury effect.

The good news is that there is little risk of syphoning back since the waste pipe from the toilet goes up high into the tank, only if it is completely filled a small amount may flow back.

The second good news is, that this only has one seacock and I sure tried to keep those at a minimum.

One down side may be that you are always going through the tank, but on the other hand keeping it in use may well be better than leaving an uncleaned tank cut off for a longer time.

The real problem is that there isn't always enough pressure by weight of the stuff, to press all the bits through the exit tube, and then it starts building up, the liquids still escaping for some while. Eventually it's clogged and you have a problem.

Some other boats with the same arrangement apparently did ok, since they had electric toilets with macerators. I, to keep things even simpler have regular manual toilets, which seem to not do to much damage to the stuff.

Both our heads were exposing the same problem. We survived the first season once we found a way to clear the clogging. We did this by hammering a wooden leak stopper into the air vent, and then pressurizing the tank via the toilet until you hear a big swoosh.

After some discussion with the yard, they installed and paid for two big Sealand T-pumps, that have absolutely no problem draining the tank. So now I'm actually quite happy with the result. Still only one seacock, stuff goes generally to the tank, and we run the pumps when we are out of anchorages and harbours.

So, don't assume that anything but real force will reliably empty your tanks.

 

[southchinasea]

Thanks to all. Once again very helpful. I borrowed a Westmarine 2002
catalogue and indeed very good explanations and schematics.
Cheers

 

[southchinasea]

Just as a follow up. I have just completed a 5 day passage on the aforementioned
friends Oyster 45 and was correct in my first posting assumption. One of his toliets does indeed discharge firstly into the holding tank. Then either (via simple lever)
a) stays in holding tank for pump out later or
b) via a fairly large diameter outlet, empties into the sea (offshore of course). Simple gravity with perhaps a little Venturi effect. He claims never to have had
a blockage since boat bought new (1997).
Just fyi.
Cheers