Siphon breaks

I understand that siphon breaks have a valuable role but found none on my boat. The manufacturer told me they "never saw the need" or something similar... that is not the structure of an explanation I find convincing. Can anyone explain why I don't need them on my NT42?

Gilhooley

Any continuous hose full of water or even partly filled such that a slug of water could start a siphon, from below the waterline to a lower point in the hull needs a siphon break.

There are descriptions of piping and applications that can be argued because of "heeled" waterline or thru hulls "occasionally" underwater that one should install a break...but as I said "argued".

The concept to me means.... unless there will be a natural air break at some point to prevent continuous siphoning...by any means...a siphon break is warranted.

In general, they are needed when a big enough loop cannot be formed, say on a bilge pump or other below the water line termination, to extend above the maximum heeling waterline, relative to the outlet, of the boat. My old Hatteras didn't have any either, just a lot of big loops. Most of the outlets were almost at the at-rest waterline, but the loops extended above the heeling line anyway.

All sea water toilets--manual and electric--that are even partly BELOW waterline need a vented loop (siphon break) in the intake...see toilet installation instructions for correct location, which may NOT be in the line between the thru-hull and the pump. One is also needed in the head discharge line if plumbed to flush directly overboard at sea. Holding tanks plumbed to discharge overboard may or may not need one.

even with a big enough loop...if a continuos waterflow is established within the hose and one end is lower than the other and assuming the higher end remains below the waterline continuously.....a siphon will form.


please...hopefully some physicist on here will tell me that at some height a siphon will break down because of something to do with gravity or molecular structure...but I believe siphons work at least to 1 additional atmosphere...33 feet? certainly higher than most of our loops...

Siphon - Simple machine

All a siphon needs to work is a liquid filled hose or pipe flow path, both ends submerged in different bodies of water or at least blocked to prevent air entry, and a height difference between bodies of water. The water will flow to the lower end. Once flowing it no longer needs to be submerged at the lower end. Rate of flow depends on the difference in height. You need to look at your plumbing on board to see where this is possible under any condition.

psneeld said:

even with a big enough loop...if a continuos waterflow is established within the hose and one end is lower than the other and assuming the higher end remains below the waterline continuously.....a siphon will form.


please...hopefully some physicist on here will tell me that at some height a siphon will break down because of something to do with gravity or molecular structure...but I believe siphons work at least to 1 additional atmosphere...33 feet? certainly higher than most of our loops...

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Where I use to work we had piping 10 ft diameter designed to use the siphon principal to reduce power required to move millions of gallons of water per hour.

33 ft is the most you can lift on the inlet side and thats if its perfectly airtight.

High Wire said:

Where I use to work we had piping 10 ft diameter designed to use the siphon principal to reduce power required to move millions of gallons of water per hour.

33 ft is the most you can lift on the inlet side and thats if its perfectly airtight.

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Thanks Archie...I think for some cases all you need to do is get the flow side liquid lower than the feed end, the flow end doesn't have to be immersed.

Like siphoning gas...just get it you your lips, lower the hose and let her rip!

Maybe with lower gas prices it will become a lost art......quite popular but a few years ago....

HeadMistress said:

All sea water toilets--manual and electric--that are even partly BELOW waterline need a vented loop (siphon break) in the intake...see toilet installation instructions for correct location, which may NOT be in the line between the thru-hull and the pump. One is also needed in the head discharge line if plumbed to flush directly overboard at sea. Holding tanks plumbed to discharge overboard may or may not need one.

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Thanks... that may or may not need one part... can you fill the detail in on that? While I've got you, I came across something you wrote about making your fresh water usable last year and it worked like a charm... thank you for that too.

Whether your toilet is manual or electric, if there's a short piece of hose connecting the pump to the back of the bowl, that's where the vented loop belongs. You'll most likely have to replace that piece of hose two that are about twice that long because the loop has to be at least 6-8" above waterline.

The Groco Model K and the higher end all china electric "thrones" don't have a separate pump assembly and bowl--no connecting piece of hose...so the inlet line between the thru-hull and the pump is the only place the loop CAN go. But because flushing will pull air into the loop, it need the air valve that 90% of owners have never heard of because it's a degradable part that's sold separately, and the teenagers in the boat stores are clueless. Electric toilets need a solenoid air valve wired to the flush button...when the button is pushed, the solenoid valve closes...ceasing flush opens it again.

Now...find the owners manual for your toilet, available from most mfrs' websites and read the installation instructions, which will include vented loop installation.

Glad the instructions for recommissioning your fresh water system worked for you.

psneeld said:

even with a big enough loop...if a continuos waterflow is established within the hose and one end is lower than the other and assuming the higher end remains below the waterline continuously.....a siphon will form.

Click to expand...

Then by definition it is not a big enough loop, nor does it extend above the then-existent waterline, which is dependent on heeled the external outlet (or inlet in this case) is to the water. It can't be filled with incoming water otherwise. Get a hose sometime and see for yourself, just like in science class.

caltexflanc said:

Then by definition it is not a big enough loop, nor does it extend above the then-existent waterline, which is dependent on heeled the external outlet (or inlet in this case) is to the water. It can't be filled with incoming water otherwise. Get a hose sometime and see for yourself, just like in science class.

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Archies explanation is clear enough if mine isnt.

psneeld said:

Archies explanation is clear enough if mine isnt.

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And Archies is identical to mine, in more detail, but identical.

High Wire said:

33 ft is the most you can lift on the inlet side and thats if its perfectly airtight.

Click to expand...

The 33 foot limit is theoretical since it is hard to get a perfect vacuum, and the 33 foot value is assuming distilled water, so the specific gravity of the liquid will change the limit.

In addition to the syphon breaks on my head. My engine is completely below the WL. Instead of a syphon break on the engine, I have fitted a vented loop. With the vent line (3/8") located on the topsides near the helm. This way it doubles as a seawater flow telltale and eliminates the possibility of the usual syphon valve sticking open or closed.

caltexflanc said:

And Archies is identical to mine, in more detail, but identical.

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And to mine...guess we are all in agreement.

Instead of a syphon break on the engine, I have fitted a vented loop.

A vented loop IS a siphon break/anti-siphon device. And putting a vent line on it instead of an air valve is a very BAD idea! As you've noted, it's a very small hose...only 3/8" (which I suspect is the OD because the nipple on the top fits the ID of a 1/4" hose.), so the same sea water minerals and salt that you don't want to clean out of an air valve quickly clog up the connection. But because it's solved any squirting problem it becomes pretty much "out of sight, out mind"... turning your vented loop into an UNvented loop that no longer has any ability to break a siphon.

Peggy's point is doubtless correct for sea toilets, but Brooksie's engine arrangement is fine. No moving parts and the flow of warm cooling water will keep it clear. It is immediately noticeable if the flow stops for any reason.

Shoalwaters said:

Peggy's point is doubtless correct for sea toilets, but Brooksie's engine arrangement is fine. No moving parts and the flow of warm cooling water will keep it clear. It is immediately noticeable if the flow stops for any reason.

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I would think of it like a pisser on the back of an outboard. You tend to keep looking at it and just stick something in it the minute it isnt. 99.9% of the time, that's all it needs.

Yes I know it isn't a siphon break on an outboard.

I believe some sort of water telltale on inboard engine exhausts like Brookside were discussed here not to long ago and we're more common than I had thought.

To look nice mant tines the discharge thru hulls would be placed in the painted water line.

Given enough time owners frequently bring enough junk on board and these sink to below the water level.

ALL these water exits need a vented loop .

If the boat heels enough to bury the discharge port , it needs a vented loop.

If all else fails, read the instructions

If you read the instructions first, fewer things are likely fail.

If it ain't broke, don't fix it

Too many people confuse "preventive maintenance" with "fix."
If you maintain it, it's a lot less likely to need fixing And the best thing about preventive maintenance is, you get to do it on YOUR terms, at YOUR convenience. Nothing ever needs fixing when it's convenient to do it.

HeadMistress said:

Instead of a syphon break on the engine, I have fitted a vented loop.

A vented loop IS a siphon break/anti-siphon device. And putting a vent line on it instead of an air valve is a very BAD idea! As you've noted, it's a very small hose...only 3/8" (which I suspect is the OD because the nipple on the top fits the ID of a 1/4" hose.), so the same sea water minerals and salt that you don't want to clean out of an air valve quickly clog up the connection. But because it's solved any squirting problem it becomes pretty much "out of sight, out mind"... turning your vented loop into an UNvented loop that no longer has any ability to break a siphon.

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What they said ....

Brooksie said:

In addition to the syphon breaks on my head. My engine is completely below the WL. Instead of a syphon break on the engine, I have fitted a vented loop. With the vent line (3/8") located on the topsides near the helm. This way it doubles as a seawater flow telltale and eliminates the possibility of the usual syphon valve sticking open or closed.

Click to expand...

Same here, I check the telltale as I untie the boat when getting underway, and it is always visible from the pilothouse when running.

I appreciate the discussion. Thank you. I was a bit ambiguous in noting my concern. Not so much the physics of a siphon (I actually taught university physics quite some time ago) but a concern over a manufacturer stating they "never saw a need"... there are implications to this that increase my prior level of (earned) pessimism around any decisions... design... diagnosis... operations... that emanate from the land-based side of the marine industry/services. My professional and academic lives force me to notice implications of decisions. Again.. appreciated.

LarryM said:

Same here, I check the telltale as I untie the boat when getting underway, and it is always visible from the pilothouse when running.

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We're talking about two different applications: engines and toilets/sanitation systems. While both may need vented loops (siphon breaks, vacuum breakers...), my advice pertaining to plumbing them correctly applies only to toilets/sanitation systems.

post #17???????

psneeld said:

post #17???????

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Ooops...I failed to notice that we weren't talking about toilets any more. Mea culpa.

HeadMistress said:

Ooops...I failed to notice that we weren't talking about toilets any more. Mea culpa.

Click to expand...

these TF threads are like minefields....

"We're talking about two different applications: engines and toilets/sanitation systems. While both may need vented loops (siphon breaks, vacuum breakers...), my advice pertaining to plumbing them correctly applies only to toilets/sanitation systems."



However bilge pumps are frequently well below the WL and do require a vented loop if the discharge is near the water line.

A submerged bilge pump discharge is a perfect start to a siphon.