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Old 17-12-2010, 01:12   #1
CFR
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Vented Loop Marine Head

Hi to all, i need you advice. I am installing a new manual head similar to a Groco K model but made in europe. The inlet valve will be operated by a footpedal.

now i am puzzled how to install a vented loop with a vacuum breaker on the intake side because i can only install in front of the pump. consequently the vaccum breaker will allways open when i operate the pump and it sucks water. I could install a amnual operated valve which has to be closed during pumpeing and openend afterwards but actually this is not a conveniennt option. Any idea ?

I could connect the toilet also to one of my 3 water tank and get freshwater but there is allways a slight danger of contamination although i am not using the tank for drinking water.


Second question:

I do not like to many thruhulls and i am thinking to use the seawater intake also as drain for the handwash bassin so i could also use some freshwater to rinse the seawater intake line and toilet. I am afraid that the open drain might disturb the pump suction and i will only get air to the suction of the pump.

Would appreciate any comments Thanks from Hamburg Germany
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Old 17-12-2010, 05:48   #2
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We use our head sink drain as the intake for the head, only with very vigorous pumping will you draw in air from the sink and if you do it hurts nothing.
If you want a vented loop on the seawater side, it goes between the pump and the bowl, not on the suction side of the pump.
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Old 17-12-2010, 06:27   #3
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Thanks for info. yes i know the setup for the vented loop but in my toilet the pump underneath the bowl is connected internally and no chance to install a loop
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Old 17-12-2010, 06:44   #4
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The vented loop/siphon break goes between the pumps outlet and the back of the bowl on the pressure/outlet side of the pump not the intake/suction side.
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Old 17-12-2010, 07:03   #5
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The pump is directly connected to porcelain bowl.
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Old 17-12-2010, 07:14   #6
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Still puzzling over my own setup.

But while searching online I have seen a solenoid operated valve on top of a vented loop. This was on the suction side as needed for the OP. Flipping a switch closes the valve. So the resting, no current draw state is open for venting.

Flip the switch, pump the head, flip the switch off.
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Old 17-12-2010, 08:18   #7
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Normally the vented loop only goes in the discharge line from the MSD. This is the line from the MSD to the overboard thru-hull/seacock. This side of the MSD system is not protected by any valves that you can control. Normally all there is in the discharge line is a "joker" valve that is made of rubber and irises open or closed with each pump of the discharge. Using sea water the "joker" valve tends to collect a crust and finally will not close properly. The Vented Loop prevents a "siphon" effect allowing seawater to flow backwards into the MSD (which is normally below sea level inside the boat) and flooding the boat.
- - The "vent" in the vented loop is usually another tiny "joker" valve orientated to allow air to enter the discharge loop but closes when there is any pressure in the discharge loop.
- - The seawater to flush the MSD bowl is controlled by a manual valve that you turn from "Flush" to "OFF" or whatever, so you do not need a vented loop in that line and in most MSD's it is not physically possible to install one.
- - With the new "holding tank" requirements, it is common now to directly plumb the MSD discharge to the holding tank (which is vented) with no vented loop in that line. But from the holding tank to the discharge thru-hull/seacock there is a vented loop to again prevent siphoning sea water back into the holding tank.
- - If your selector "Y-valve" is between the holding tank and the MSD it starts to get complicated as you end up with maybe two vented loops. One for the MSD discharge directly to the sea and another from the holding tank discharge to the sea. There is another "Y-valve" after the holding tank that allows selection of holding tank discharge directly to the sea or up to the deck pump-out fitting.
- - In order to simplify the mess, I plumbed my MSD's directly to the holding tanks and then use a macerator pump and vented loop to discharge the holding tank to the sea. There is only one "Y-valve" and it selects the holding tank discharge to the macerator pump and overboard or up to the deck pump-out fitting.
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Old 17-12-2010, 08:24   #8
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I will say that we have no vented loop on either the water side of the discharge side on ours. the rim of the bowl is 2" above the waterline and the discharge goes up to a tank that is above the waterline. seeing as the tank is vented it serves the loop purpose. the loop isn't needed if you have the top of the bowl high enough.
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Old 17-12-2010, 08:28   #9
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We have a vented loop on the intake side, between the thru-hull and the pump which is also on the toilet bowl assembly. A small tube attaches to the top of the loop and runs to a small fitting on the face of the counter adjacent to the toilet. To pump, one covers the fitting with ones thumb which disallows air to be drawn into the system. On using the sink discharge as a raw water source, simply insert a plug in the sink drain and, if necessary, run a small bit of water into the sink to cover the plug. It works for us.


FWIW...
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Old 17-12-2010, 08:29   #10
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Just be sure that your measurement takes into account where the waterline is located when the boat is heeled over under sail (mono-hull - cat's can ignore this).
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Old 17-12-2010, 09:06   #11
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Originally Posted by osirissail View Post
Just be sure that your measurement takes into account where the waterline is located when the boat is heeled over under sail (mono-hull - cat's can ignore this).
I've always worked on the assumption that if the boats heeling over under sail, that means I'll be on board sailing it. If that's the case, I'll notice the water spilling out of the toilet. even without the pump mechanism in line, the 3/4" hose leads such a tortured route of ups and downs that little water comes out of it anyway without pump assistance.
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Old 17-12-2010, 10:18   #12
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While we're on the subject of vented loops for discharge via thru-hulls.

Install a anti-syphon valve on the discharge hose for your bildge pump. Loop the discharge hose above the water line.

More than one boat has taken on water when the bilge pump is activated while the boat is heeled over. When the pump has completed its task and shuts off, seawater is syphoned back into the boat.
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Old 17-12-2010, 14:02   #13
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Originally Posted by CFR View Post
similar to a Groco K model but made in europe.
Sorry missed the part about Groco Model K or "similar". Those pumps do not require a vented loop in the intake path like most other manual heads do. Those pumps are pretty fail safe, unlike some of the cheaper ones. If, it is in fact like a Groco Model K.
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Old 18-12-2010, 09:21   #14
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. . . Install a anti-syphon valve on the discharge hose for your bildge pump. Loop the discharge hose above the water line.

More than one boat has taken on water when the bilge pump is activated while the boat is heeled over. When the pump has completed its task and shuts off, seawater is syphoned back into the boat.
Double second that - Been there, done that, had the high water alarm go off - any hose, etc. that starts below the waterline and exits below the water line needs a siphon break (Vented loop).

For Sailmonkey - when sailing in the ocean or long overnight passages you will be heeled over for a very long time and while maintaining watch or fighting big seas - you have little or no time to be worrying about a back siphoning MSD. More than a few boats have been caught in deep (pun intended) do-do when the MSD is not shut off properly or the Vented Loop valve malfunctions.
- - Which brings up the subject that all Vented Loops are not created equal. Just like bilge pumps. Some brands like Forespar have vents that cannot be serviced or checked or fail easily. The Vetus brand seems to be a really reliable brand even though it costs more.
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Old 20-12-2010, 07:48   #15
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Some brands like Forespar have vents that cannot be serviced or checked or fail easily. The Vetus brand seems to be a really reliable brand even though it costs more.
Really? I clean and service Forespar siphon breaks on a quite often. The black cap simply un-threads and the duck bill / siphon break insert simply pops out for cleaning. Takes all of about three or four minutes..

Forespar Duck Bill Element




That being said the most reliable siphon breaks I know of are made by a small company in Florida called the Scot Pump Company. I have never had one fail or leak, they just seem to work and work well. I don't use them on heads though unless I can figure a way of piping the breaker into a plastic loop. I don't generally prefer stainless loops in an MSD systems.

Scot Pump Replacement Element


Scot Pump Vacuum Breaker Assembly
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