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Old 14-01-2019, 09:45   #1
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Raw water return air bubbles exhaust

I have broke the connection for the little plastic pipe. Check the attached image. If I understand it is to not have air in the top of pipe curve.
If I clog it temporally could i have some damage or problems?
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Old 14-01-2019, 09:48   #2
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Re: Raw water return air bubbles exhaust

Do not clog it. Its purpose is to prevent a siphon. If you clog it, then you might have a siphon if the seacock is open and this will flood your engine with sea water.
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Old 14-01-2019, 10:00   #3
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Re: Raw water return air bubbles exhaust

Ok. Thank you.
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Old 14-01-2019, 20:53   #4
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Re: Raw water return air bubbles exhaust

I used one rivet to solve the problem. I took the metal part out to have the aluminium part as pipe. As first I drilled a hole in existing connection. And then I hammered with plastic hammer the rivet to fit in the hole. Before that I used drilling machine as lathe and a file to grind rivet to get just a little of cone shape.

I am writing now because I would like to ask for siphon explanation?
I did attach image where is also other siphon on bigger gas pipe. They are connected together with a small pipe which connection I have fixed.
I have to check all this pipes if there is some clog.
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Old 14-01-2019, 21:23   #5
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Re: Raw water return air bubbles exhaust

The purpose of a vacuum break is to let air into the line ONLY when water is not being pushed through it. The hoses then become vents. The break must be above the waterline, otherwise the valve would not open. If the valve is clogged, you have a solid hose.

Imagine you have a lose solid hose connected to an open seacock. The end of the hose is held above the waterline. No water comes out, right? The hose is filled as high as the water line - basic physics....
Now, slowly lower the hose. As the end of the hose comes level with the outside waterline, the water in the hose rises to the tip. As you continue to lower the hose, water comes out faster the more you lower it.


Now if you connect that hose to your water injection port (assuming the port is below the waterline) where does that water go? It fills your exhaust system up until the water backs into your engine and ruins it (assuming your exhaust manifold is also below the waterline).

So the purpose of the siphon break is to let air into the line so the water on your intake side can’t ‘climb the hill’ and run into your exhaust when the raw water pump isn’t pushing it. If the siphon break is clogged (solid hose scenario again), you could have that line run all the way up the mast and back, as long as the end off the hose is below the waterline, the weight of the water falling ‘down’ the hose to the end will be greater than the weight of the water on the ‘up’ side, causing a siphon

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Old 16-01-2019, 18:50   #6
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Re: Raw water return air bubbles exhaust

To make all clear I have marked points from 1 to 9 on attached image.

Before we begin. Is the drawing without logic mistakes?

I am not sure if no. 5 and no. 4

Do they have to be under water line or not when boat is inclined to the point as it is on image?
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Old 16-01-2019, 23:11   #7
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Re: Raw water return air bubbles exhaust

Perfect logic.

The vent line 2-5 will cause segment 5-6 to drain into the muffler when you kill the engine. Your vent line 2-4 will do the same for segment 4-9, allowing it to drain out the exhaust.
With air in those segments, allowed in by the vent/siphon break, there is no weight of water to ‘pull’ the water from 4-6 and 5-7 and siphon.

Your setup will work so long as you stop the motor and allow a bit of time in a more vertical position - the vent can’t be under water while you stop it - you have to let air into the lines.
After you do so, that heel angle will be fine - any little bit of water that came in the vent would still have an uphill climb up a dry, air-filled tube - just not going to happen.

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