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Old 18-01-2007, 21:50   #1
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Exhaust anti-siphon etc.

My exhaust travels from the exhaust injection elbow down into what I guess is a wet exhaust lift muffler (a fibreglass box) and then up and out the boat.

I'm replacing the exhaust hose (from box to thru-hull) and want to confirm:

1) The exhaust hose must loop up 18" above the (heeled) waterline (to avoid water coming in from the thru-hull I assume)?

2) I don't think you need an anti-siphon vent in that?

3) You need an anti-siphon in the hose that feeds the water to the exhaust injection elbow, right? There isn't one now, so would I just put a Y in the hose and lead it somewhere 18" above the heeled waterline and terminate it with an inverted U and a check valve?

Thanks,
Ty
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Old 18-01-2007, 22:06   #2
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here's a photo from the gallerythat should help.........................._/)



and another.....................

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Old 18-01-2007, 22:18   #3
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Geez Del, how'd you find those so quick.

I had a look, but had no joy.

Dave
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Old 18-01-2007, 22:31   #4
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Thanks - great images - I'll be following Figure 1 of the 2nd image but regarding that siphon break - my engine is right in the centre of the salon (covered up with a big seat) so I can't just go straight up high enough. Would I lead that whole water line in a big loop to where I can get high enough? Or can I just make a Y in it and lead one part over and up to a check valve (which I think would still break a siphon)? I should draw this as I think it's kinda confusing!
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Old 19-01-2007, 00:00   #5
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The first question is were is the injector line of the exhaust in relation to the waterline????

A "Y" with a check valve would work providing the valve was very small so if it happen to fail it wouldn't cause a big mess. A siphon loop is basically a check valve T'ed in the line. It's just that it's a rubber squeese valve like in the toilets, vs a mechanical valve like for a thruhull. A squeese valve will only open enough to just let the air pass. A mechanical valve will open all the way if up side down and will leak until it gets shut.

If you were to take a siphon loop and attach it to the end of the "Y" and cap the other end that would be a safer set up. Or, if the valve were long enough on the loop, one could cut it off and attach it to the end of the "Y".


Dave, we ole salts of the forum baiscally built this place.
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Old 19-01-2007, 00:16   #6
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Hey Del,
The injector line is below the waterline.
The "safer set up" you mention is how I'm thinking - a T in the injector line (below the waterline) with a thin hose running from it up and terminating in a squeese valve up above the water line like you describe. I guess it could actually even exit outside to avoid the leak issue...
Thanks again, Ty
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Old 19-01-2007, 01:00   #7
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If you use a very small line (1/8") that would be like the "type H" in the top picture. Then you wouldn't need a valve.

The main thing is to put the "T" closer to the exit end of the loop so if the residual water that runs back it will run into the exit end and out the exhaust.
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Old 19-01-2007, 08:12   #8
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If you do not put a valve, then, like "type H", water will continually flow out from the pressure in the system, right? I guess with a 1/8" line it won't be much but can the loss of pressure and/or coolant be a problem? It's just a little 20HP Yanmar... Might actually be a good indicator that the coolant is flowing...

Good point about the position of the "T, that's what's I'll do.
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Old 19-01-2007, 11:02   #9
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Aloha Tyrol,
There shouldn't be any coolant in that line. It should be seawater.
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Old 19-01-2007, 11:13   #10
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Sorry, that's what I meant... If some seawater amd pressure gets diverted to the vent from the exhaust injector in that a problem?
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Old 19-01-2007, 14:55   #11
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Judgements are hard to make without actually doing the work. But as long as the motor keeps it proper operating temperature, that's what is important. If it's expelling too much water one can meter it down.

But 1/8" is pretty small to start. If it's a concern I'd go back to cutting the valve from a loop and install it at the end.

Is your motor raw water cooled or does it have a heat exchanger??????
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Old 19-01-2007, 15:34   #12
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It's raw water cooled unfortunately... I've tried to find a reasonably priced heat exchanger without too much luck. It's a Yanmar 2GM20 (or QM?).
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