Genset Vented Loop

[Lenihe]

Recently the generator vented loop has started discharging seawater through the syphon valve while it is running. The rubber valve is in good condition.
Does anyone have any suggestions as to what has changed and how to fix it?
It flows onto a run of wires which is also a concern.

Thanks in advance.

Len
Selene 43

[GordMay]

Greetings and welcome aboard the CF, Len.

[a64pilot]

Pretty much can't be in good condition, it leaks now. I'd replace it.

[Sailmonkey]

Depending on the manufacturer.....I'd guess the duckbill has gotten hard and gave up. Some you can by a replacement for, others you just replace the whole thing.


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[exMaggieDrum]

Some vented loops don't have a duckbill valve at all. They have piece of clear tubing that goes to the bilge. You can have it on a vent with a duckbill too. But it should not be spitting water out constantly. I am not sure what would cause that other than a blockage downstream or too much pressure/flow from upstream. Just seems odd in my experience.

[a64pilot]

Originally Posted by exMaggieDrum

Some vented loops don't have a duckbill valve at all. They have piece of clear tubing that goes to the bilge. You can have it on a vent with a duckbill too. But it should not be spitting water out constantly. I am not sure what would cause that other than a blockage downstream or too much pressure/flow from upstream. Just seems odd in my experience.

I've even seen some use clear aquarium tubing to have a "pee" tube similar to an outboard motor (remove the valve) I believe when I install the water separator on my generator I may do that, so I'm sure it's getting water flow, plus of course as this is just an open tube, nothing to stick or wear out too.

[CarlF]

Feel around with a piece of stiff wire for any weed that might be keeping the rubber from seating.

What is the brand of valve? (a picture would be better)

If it's in a location that easy to replace, I'd just replace it. Also check the others on your boat. One that is stuck closed could sink your boat by allowing a siphon. It's really unlikely but why take the risk?....

I like the Forespar ones as they are Marelon so have no corrosion and spare duckbill rubber pieces are available (i carry a few spare duckbills).

[svHyLyte]

If you are getting back-flow through the vent on the "vented loop", it is likely you have an obstruction between the vent and the through hull that is preventing the free discharge of cooling water which "back's up" in the loop circuit. If the generator is not run often (most aren't), you could very easily have critters "growing" in the discharge line, not unlike the build-up of material in the arteries. One can check, to some extent, by freeing the discharge side of the loop from the vent and inserting a simple cone nozzle from a garden hose into the hose end. If the discharge hose is "clear", water from the garden hose should blow through quite easily, if not, it too will back flow into the boat around the cone. Should that happen, you might try closing the sea-cock at the thru-hull, draining as much water out of the discharge line as possible (if necessary using a 1/4" diameter tube inserted into the discharge line as far as possible and the suctioned out with your shop-vac, and then refilling the discharge hose with a solution of Barnacle Buster or RydLyme and water and allowing that to site over night. Either of those materials will dissolve any hard-shell critters and kill off any other growth. Then, open the sea-cock, and wait another day (the mixture will clear whatever may be growing on the ocean-side to the sea-cock). Finally, reinsert the cone end from your garden hose, and blow out the line with fresh water. If "growies" are the obstruction, the foregoing will clear them out pretty effectively and get you back in business. (BTDT--Got the T-Shirt)

FWIW...

[Lenihe]

I have several vented loops with the same duckbill set up. When I switch them the problem still persists.
The obstruction theory sounds the most likely at this point so will try that in the next couple of days.
Thanks for the suggestions.