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Old 04-18-2021, 11:46 PM   #1
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vented loop maintenance

On November 1, 2020, I last saw my boat, as I had returned Retreat to her winter residence on Vancouver. All was well. Fuel and water were full, Black water was empty, she was plugged in with heaters on the lowest settings. Charger and water heater on in the ER to keep that area warm.
What could fail?
This morning I made the trek to remove Retreat from that winter moorage and bring her home to Saltspring. Beautiful warm, sunny, calm day. Perect for a crossing of Georgia Strait.
On boarding, I could hear water running. I checked the bilge in the forward cabin. nice and dry, but the sound of running water was louder. I checked the ER. Not as loud, and no sign of high water. I then checked the galley. The floor opens above the holding tank. All the fittings are right there, and the vent line had parted just after the hose clamps. A stream of water was draining from the top of the tank to the bilge. But I had left the tank empty???
I didn't take long to decide that the anti siphon had failed. I had recently renewed those hoses and the anti siphon, with one like this: https://www.ebay.ca/sch/i.html?_nkw=...2a6a39bdee1656
from the top of the fitting, a lightweight hose drains any spittle into the bilge. I blew on that hose and couldn't get any air to pass through it. SO I took it off and used a coat hanger to poke through the blockage and open it up, then ran the pump and noted a good strong stream. All good now.
Before putting in the new hose and siphon break, I had never had such a failure. There are other, older siphon breaks aboard, all of which are performing properly. This one is now add as the regular maintenance item.
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Old 04-19-2021, 04:35 AM   #2
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. This one is now add as the regular maintenance item.
Certianly a good reminder to all!

I will add something else here: After cleaning, be SURE to put the rubber duckbill "valve" back in the correct position. It's easy to accidentally place it upside down, which would entirely defeat the purpose of the vented loop and INCREASE the risk of siphon!
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Old 04-19-2021, 05:24 AM   #3
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Good catch and reminder. Is the through hull valve working OK? How high above the WL is the siphon break?
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Old 04-19-2021, 09:15 AM   #4
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Keith
Good catch and reminder. Is the through hull valve working OK? How high above the WL is the siphon break?
Tom
As usual, you have seen through the details to the real issue, I didn't close the through hull! Hard to do on that line, as it is located in a very awkward spot. When I tried to close it yesterday, I failed. It requires the use of a 12 yr old helper, in order to get a very skinny arm into the space, with the wrist and hand strength of a very fit body builder, to get the valve arm to move. I have neither of those attributes.
The siphon break is right up as high as it can be, under the saloon floor.
I have recently added a PVC valve to the bottom of the black tank, as I had a fitting failure at that location, which is accessible. And no, I hadn't closed that one. It will not be forgotten next fall. But had either of those valves been closed, I would never have figured out the failure of the siphon break. Likewise the failure of the vent line, had that not failed, I would have tried to use the black tank, knowing it was left empty, found it full, and had a mystery to solve.
Good luck, rather than good management.
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Old 04-19-2021, 09:43 AM   #5
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I didn't take long to decide that the anti siphon had failed...

The "running water" had to be coming in from somewhere, making the real source of your problem not a failed anti-siphon loop, but YOUR failure to close all thru-hulls before leaving the boat! Thru-hulls left open when no one is aboard is a leading cause of boat sinking in their slips.

And what is this "from the top of the fitting, a lightweight hose drains any spittle into the bilge????"

Apparently you're relying on that instead of a proper air valve in the nipple on the top of the loop, common instead of a proper air valve on vented loops installed in toilet discharge lines to deal with the squirting from liquid being PUSHED through a line connected to a below-waterline DISCHARGE thru-hull, which is a bad idea because that line is so small that it quickly becomes clogged by waste and sea water minerals, turning the vented loop into an UNvented loop that no longer has any ability to prevent a siphon. Then you compounded your error by plumbing it to drain into the bilge instead of an above waterline thru-hull.

Tank vent thru-hulls are well above the waterline, so it splitting should have nothing to do with water coming in...a split in the "vent" line connected to the vented loop would increase the flow of water into your bilge. So which vent line was it that had parted company--the tank vent line or the one that drains into the bilge?

--Peggie
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Old 04-19-2021, 09:59 AM   #6
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But had either of those valves been closed, I would never have figured out the failure of the siphon break.

The siphon break didn't fail. You were unable to blow air through it because sea water mineral buildup from the water coming in through the open thru-hull all winter had blocked it and most likely the hose it was in too.

What type of PVC valve did you install in the bottom of the tank to replace a cracked fitting?

--Peggie
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Old 04-19-2021, 10:04 AM   #7
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Quote:
Originally Posted by HeadMistress View Post
I didn't take long to decide that the anti siphon had failed...

The "running water" had to be coming in from somewhere, making the real source of your problem not a failed anti-siphon loop, but YOUR failure to close all thru-hulls before leaving the boat! Thru-hulls left open when no one is aboard is a leading cause of boat sinking in their slips.

And what is this "from the top of the fitting, a lightweight hose drains any spittle into the bilge????"

Apparently you're relying on that instead of a proper air valve in the nipple on the top of the loop, common instead of a proper air valve on vented loops installed in toilet discharge lines to deal with the squirting from liquid being PUSHED through a line connected to a below-waterline DISCHARGE thru-hull, which is a bad idea because that line is so small that it quickly becomes clogged by waste and sea water minerals, turning the vented loop into an UNvented loop that no longer has any ability to prevent a siphon. Then you compounded your error by plumbing it to drain into the bilge instead of an above waterline thru-hull.

Tank vent thru-hulls are well above the waterline, so it splitting should have nothing to do with water coming in...a split in the "vent" line connected to the vented loop would increase the flow of water into your bilge. So which vent line was it that had parted company--the tank vent line or the one that drains into the bilge?

--Peggie
Peggie
Thanks for your attention. First, I agree that the through hull being open invited the problem.
There are 2 vents. the one that parted is the one that vents the tank. It parted at the tank end. The other one vents the loop, It drops through the floor boards over that part of the bilge and unless the boat is filling with water, will be above the inside waterline.
Please tell me why the guy who installed this vented loop drain put a drain line on the loop itself, and why he directed that line into the bilge. Too long an explanation, but I installed the vented loop a few years ago, when I replaced a bunch of holding tank plumbing. I did not put a line on the vent on the top of the loop. It was left as it came from the chandlery, as show in the diagram at post #2 from ScottC.
When I had a new generator installed, the tech put an identical vented loop on a hose coming from the generator. Due to space constraints, that loop was attached to the one on the sanitation line and both were given lines from those vents to the bilge. Should there be lines on those vents? If so, those should then go to above WL thru-hulls?
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Old 04-19-2021, 10:20 AM   #8
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But had either of those valves been closed, I would never have figured out the failure of the siphon break.

The siphon break didn't fail. You were unable to blow air through it because sea water mineral buildup from the water coming in through the open thru-hull all winter had blocked it and most likely the hose it was in too.

--Peggie
That is what I figured, and isn't that a failure? The only reason there was water at that location was because it wasn't working, not allowing air to enter through the valve at the top, releasing the water to settle to the level of the outside waterline. The discharge hose wasn't blocked. Isn't blocked. OR am I missing something else?

"What type of PVC valve did you install in the bottom of the tank to replace a cracked fitting?"
Not to replace anything, just to have a positive closure at the exit of the black tank, this kind, in 1.5":https://www.lowes.ca/product/pvc-sch...alve-330615399
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