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Old 20-12-2012, 17:15   #16
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Re: Anti siphon loop vent failure

Are you talking about the water intake for the head or the water injection line for the exhaust? They usually fail the other way so that the vent line is plugged and the water siphons back up and into the exhaust and eventually possibly into the engine. Instead of a siphon break device I just have a hose attached to a T in the water injection line for the exhaust. The hose is at the high point in the injection line and goes to a cockpit drain near the top. It both effectively breaks any siphon and provides a distinct sound letting me know that water is being pumped when the engine is running.
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Old 20-12-2012, 17:16   #17
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Re: Anti siphon loop vent failure

I forgot to mention that the siphon break is a maintenance item. Should be cleaned and checked at least once a year.
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Old 20-12-2012, 17:27   #18
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Re: Anti siphon loop vent failure

I removed the rubber vent and replaced it with a small diameter copper tube that exits into the centerboard trunk, just below the level of the cockpit sole. Now, when I want to confirm that the seawater pump is working I just lift up the board covering the centerboard slot and watch the stream of water shooting out. It never plugs, and it is refreshingly simple to check.
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Old 20-12-2012, 17:28   #19
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If the vent fails to open, even if above the waterline, it can and will siphon water in. But what vent are you talking about?
The vent line for the raw water pump heat exchanger line. Our head has a direct line from thru hull valve to the pump on the head. No vented loop. In fact none of oyr last 3 boats had a vented loop on the water feed line for the head.
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Old 20-12-2012, 17:37   #20
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Re: Anti siphon loop vent failure

Theoretically you can get away without vented loops on the head and the engine cooling if you always remember to turn off the intake sea cock. I have always set up my boats so that the head seacocks could be turned off and that was part of our routine after every use--might be too much work for some people, but I previously woke up in the middle of the night to gurgling water sounds only to leap out of bed into water over the floorboards, coming in through the head. Decided to end that problem once and for all by insisting the intake be shut after every use. Now with a composting head there are no through hulls or valves to worry about.
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Old 20-12-2012, 18:10   #21
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Re: Anti siphon loop vent failure

With my memory I wouldn't dare to do away with the engine siphon break. New engines are very expensive.
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Old 20-12-2012, 18:14   #22
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Re: Anti siphon loop vent failure

I agree on the engine siphon break, mainly because I also like to know the water is flowing and you can set it up so there is a telltale stream going somewhere for you to notice. The problem is those engine cooling siphon breaks are very prone to clogging and then you are back to no siphon break. I can't remember where I read it, but I think it was a surveyor who said that most of the siphon breaks he examined were not functioning properly.
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Old 20-12-2012, 18:17   #23
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Re: Anti siphon loop vent failure

I know. That's why I like to expound on the fact that they are "Maintenance Items". Many people don't even know they are there until they have engine problems.
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Old 20-12-2012, 20:02   #24
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As far as a sign your pumping water i check periodically by glancing over the side and seei g if waters coming out the exhaust in a good rate
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Old 20-12-2012, 21:39   #25
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Re: Anti siphon loop vent failure

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Originally Posted by Dulcesuenos View Post
I am curious if the actual vented loop pipe is above the water line, would this still allow water in the bilge in the event of a vent failure?

Mine appear to have the hose clamped to the pipe roughly 6" above the water line, placing the actual vent much higher.
If the valve freezes in the open position no water can siphon when the motor is off but it will spew water when the motor is on and the system is pressurized.

If the valve freezes in the closed position no water escapes when the motor is on but water can siphon when the motor stops and the system pressure goes below ambient.
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Old 21-12-2012, 02:09   #26
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Re: Anti siphon loop vent failure

I think there seems to be a thread of confusion in this discussion, the siphon break is designed to open under low pressure and allow an air intake which ensures water will not the gravitate back to the exhaust manifold and cause serious engine corrosion. I recently replaced an old style Volvo brass siphon break with a new Nanni diesel after market one which is non metallic and easy to service, it was a simple job with some new hose from the water pump to the siphon the only other need as the mounting was a little different for the new break.
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Old 21-12-2012, 02:39   #27
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Re: Anti siphon loop vent failure

For those with a PSS, one can run a hose from the top of the loop (above the waterline) down to the fitting on thr PSS (Packless Seal System). This way it serves two purposes and it will not plug.
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Old 21-12-2012, 02:45   #28
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Re: Anti siphon loop vent failure

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Originally Posted by delmarrey View Post
For those with a PSS, one can run a hose from the top of the loop (above the waterline) down to the fitting on thr PSS (Packless Seal System). This way it serves two purposes and it will not plug.
Good idea

EDIT: I think?
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Old 21-12-2012, 06:21   #29
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Quote:
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For those with a PSS, one can run a hose from the top of the loop (above the waterline) down to the fitting on thr PSS (Packless Seal System). This way it serves two purposes and it will not plug.
Except then it's no longer a siphon break. One must introduce air into a fluid system to break a siphon!!!
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Old 21-12-2012, 09:54   #30
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Re: Anti siphon loop vent failure

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Except then it's no longer a siphon break. One must introduce air into a fluid system to break a siphon!!!
It seems to work on mine just fine. When I shut off the motor the air left in the exhaust rises back up the down-side of the loop allowing it to go up into the tube that feeds the PSS and drains back to sea level.

I have to do it this way b/c sea level is right at the top of my motor, other wise I'd be getting feed back from my stern tube.
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