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Old 01-25-2018, 10:04 PM   #1
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Anti siphon on exhaust water line

My fellows TFers, greetings from the frozen land.
This morning I was curing my lack of boat by reading some docs from vetus. I have a waterlock from vetus on my exhaust line. In their doc they mention that an anti siphon valve should be set on the water line at a minimum of 40cm above the waterline. My exhaust water injection point is at the water level or few cm above and my ER does not allow to have an anti siphon valve at the mentioned level.
So the following questions
Is it required (or best) to have an anti siphon on the water injection line?
If yes what do you think about the 40cm?
How about the waterlock setup?
Note: my setup has a flap on the exhaust to avoid water ingress, a 1 to 1.5 feet rise before the exhaust output and the waterlock 1 foot below the exhaust from manifold. Never had an issue cruising in fresh water but thinking about this (or over thinking about this )in sea waves.

L
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Old 01-25-2018, 10:19 PM   #2
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The issue has to do with water syphoning through the raw water pump into the exhaust of the engine after shutdown. Do you have an exhaust riser that prevents the water from syphoning? Is there a lift muffler between the exhaust elbow and transom exhaust outlet?

Ted
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Old 01-25-2018, 10:25 PM   #3
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Exhaust line is as follow:
From manifold the elbow with injection is going down.
1 foot below there is a waterlock (if I am not mistaken, 10.5l capacity)
From the waterlock go straight to an elbow
The elbow it aroung 16 inches high
Then straight to the exhaust through hull
Then out a 90 degre to right and 2 feet to the exhaust flap and end. (Exhaust end is on port side)
Exhaust output is at around 3 inches above water when fully loaded.

L
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Old 01-25-2018, 10:54 PM   #4
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It would help to describe the elevation. Does it go down from the exhaust manifold to waterlock, then up to an elbow, then down hill to where it exists the transom? What is the drop from the manifold to the waterlock? What is the rise to the elbow? Where is sea level in relation to the water injection point, the waterlock, and the elbow?

Ted
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Old 01-25-2018, 11:00 PM   #5
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It would help to describe the elevation. Does it go down from the exhaust manifold to waterlock, then up to an elbow, then down hill to where it exists the transom? What is the drop from the manifold to the waterlock? What is the rise to the elbow? Where is sea level in relation to the water injection point, the waterlock, and the elbow?

Ted
From manifold to waterlock drop is around 1 foot.
Then from waterlock it rises 16 inches up then same down to the output.
Water injection point is more or less at sea level so water lock 1 foot below elbow after 16 above and output 3 inches above sea level
(Approximately at 1 inch or 2 precision)

L
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Old 01-25-2018, 11:14 PM   #6
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If the injection point is more or less at sea level and the elbow after the waterlock is at or above the manifold, it would be possible to fill the waterlock with water and then have the excess go back into the exhaust manifold. Consider trying to start the engine; it turns but doesn't start. While it's turning, the water pump is running and filling the exhaust system.

A syphon break would be a very good idea. There are 2 types. One goes before the raw water pump. One goes after the raw water pump. Both types work well.

Ted
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Old 01-25-2018, 11:28 PM   #7
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Ted,
Do you have a brand or model fo the two types of siphon break? I am not happy with my setup and looking to improve it.
What I have now is a U loop up in the ceiling of the engine room with a Scot vacuum breaker. From time to time, the Scot vacuum breaker sprays water which I want to eliminate.
Thanks
Henry
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Old 01-26-2018, 07:19 AM   #8
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Ted,
Do you have a brand or model fo the two types of siphon break? I am not happy with my setup and looking to improve it.
What I have now is a U loop up in the ceiling of the engine room with a Scot vacuum breaker. From time to time, the Scot vacuum breaker sprays water which I want to eliminate.
Thanks
Henry
Hi Henry,
Is your syphon break on the suction or pressure side of the pump?

Ted
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Old 01-26-2018, 07:56 AM   #9
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Siphon break can not be placed in sea water pump suction line. In that case it will feed air to the pump.

Siphon break is critical if the injection point on the exhaust mixer is below the water line. If injection point is above water line, then no need.

Siphon break generally mounted in the line between last heat exchanger an mixer injection point, but can be anywhere between pump and mixer.

Lou- Once you splash, use a water level to measure exact elevation of your injection point. Good chance that it is higher than WL.

Water lift muffler is good protection from water backing up from tailpipe, but will not prevent weepage through pump if inj point is below WL.
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Old 01-26-2018, 08:27 AM   #10
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Siphon break is critical if the injection point on the exhaust mixer is below the water line. If injection point is above water line, then no.
+1

Lou, determine WL elevation to confirm or allay your concerns.
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Old 01-26-2018, 08:32 AM   #11
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Siphon break can not be placed in sea water pump suction line. In that case it will feed air to the pump.
There is a syphon break that closes on vacuum instead of pressure. The poppet valve is pulled closed by pump suction and opens when the pump stops and suction is reduced.

Ted
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Old 01-26-2018, 08:37 AM   #12
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There is a syphon break that closes on vacuum instead of pressure. The poppet valve is pulled closed by pump suction and opens when the pump stops and suction is reduced.

Ted
Also one can run a line from the siphon break to the top of the water lift muffler.
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Old 01-26-2018, 09:05 AM   #13
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Thank you guys I will precisely measure the injection point in regards to the water level.
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Old 01-26-2018, 09:54 AM   #14
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Quote:
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There is a syphon break that closes on vacuum instead of pressure. The poppet valve is pulled closed by pump suction and opens when the pump stops and suction is reduced.

Ted
To break a siphon, device has to open under vacuum. If a vacuum did not exist a siphon would not occur. Never seen what you describe on a marine engine. But I learn new things every day.
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Old 01-26-2018, 11:02 AM   #15
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Also one can run a line from the siphon break to the top of the water lift muffler.
+1.

Here’s how mine looks, with a Vetus anti-siphon valve above the waterline. The blue hose irrigates the prop shaft tube/cutless bearing.
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Old 01-26-2018, 11:06 AM   #16
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To break a siphon, device has to open under vacuum. If a vacuum did not exist a siphon would not occur. Never seen what you describe on a marine engine. But I learn new things every day.
From what I remember, the poppet valve is spring loaded open. The pump creates a significant vacuum which pulls it shut. When the engine is turned off, the vacuum is less without the pump's flow suction and the valve opens. The spring / required suction on the poppet valve is adjustable. Seen them on smaller sailboat engines, so maybe that's why it seems odd.

Certainly using the anti syphon U with a very small breather line to the exhaust seems a better choice with no moving parts. An 1/8" line will allow a very small amount of air in the raw water system, but quickly break the suction syphon on shutdown.

Ted
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Old 01-26-2018, 11:16 AM   #17
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+1.

Here’s how mine looks, with a Vetus anti-siphon valve above the waterline. The blue hose irrigates the prop shaft tube/cutless bearing.
Assuming that's after the water pump as it pressure feeds the shaft tube.

In that application you really don't want to feed the syphon break down into the lift muffler. It's creating another syphon path. Ideally the vent hose goes only horizontally to its point of discharge, often out the hull.

Ted
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Old 01-26-2018, 11:27 AM   #18
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[QUOTE=O C Diver;630550] It's creating another syphon path. /QUOTE]

Won't happen in Angus's case as once engine shuts down drainage to nearly empty water lift of a pint or two of water occurs, thus breaking any latent suction. Mine's nearly identical.

PS - SIPHON
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Old 01-26-2018, 11:32 AM   #19
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Assuming that's after the water pump as it pressure feeds the shaft tube.

In that application you really don't want to feed the syphon break down into the lift muffler. It's creating another syphon path. Ideally the vent hose goes only horizontally to its point of discharge, often out the hull.

Ted
Also, there’s a valve in the Vetus that only opens when the pressure is removed, thus breaking the siphon.
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Old 01-26-2018, 11:49 AM   #20
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for general consumption...

Vetus comes in several styles...

some have a small rubber valve, some dont.
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