Engine anti-siphon vent

Related to another thread where we got to talking about water coming from the anti-siphon vent through hull.

I tried the method mentioned in Calder's book; to vent the loop higher than the highest point in the exhaust system. I still got water coming out of the hose. My exhaust hose is looped up to the top of the port cockpit locker; I had to hold the hose 3ft higher to get the water to stop. Doesn't appear to be practical to vent that way...

Why do you want it to stop?

Unless all the water is coming out of the vent, there is really no reason to have it stop coming out. It provides a good indication that the engine is pumping water correctly for the cooling system, and tells you if the vent is cloged and needs to be cleaned out so you don't flood the engine. As long as it is going overboard I am confused as to why you are trying to fix something that is not broken.

The real issue here seems to be that the vent may be placed in a poor location?

My Anti-siphon lessons Learned

I really am not grasping what your question relates to. If you're referring to the check valve/ 180 deg assembly it has but one function. When your engine is running the discharge water from the heat exchanger is passing thru that set of hoses. When the source of water from the Pump/ Exchanger stops the check opens and whatever water is in the line would flow/ drain down and thru the mixing elbow and into the exhaust.
In what state are you getting water flowing out the Anti-siphon line?
I have recent, relavent experience that the Anti-siphon does in fact work. I had a rebuilt/ new-to-me 3HM35F installed last Spring. The fellow who did the install for me/ actually two guys involved, the mechanic and an acquaintance who did the engine bed mods to accomodate the much larger engine/ bellhousing.
Our mechanic friend who had pulled the 2GM20F had not remembered disconnecting the anti-siphon hoses and setting them off to the side. The 3HM35F had come in the crate with a short jumper hose between the heat exchanger water outlet and the mixing elbow. The several weeks elapsed between the time of the 2GM being pulled and him getting back to the install after the glassing work was completed, he obviously forgot the external hosing.
After launch I would guess the engine ran for no more then 15 minutes while we did a check for leaks and then motored over to her Slip. The next day I was on the boat doin' whatever and the mechanic happened along. He wanted to hear the new engine run. Turn key, hit button and only a millisecond of starter sound. I went below to open things up, got a light and pretty soon recognized what was amiss. Flipped the decompression lever set and had him roll the engine over. She cleared herself and started right up. Later checked the sump and no water had gotten into the oil. And did an oil change soon therafter since she was freshly rebuilt.
What had happened, well, exactly what that anti-siphon set-up is meant to guard against. Without the anti-siphon loop installed, after shutdown and cooldown there will be negative pressure created in that relatively short length of hose between the mixing elbow and the ready source of water laying in the wet muffler. Also recognize there's additional volume of water beyond the muffler that's been pushed out there by the force of the exhaust. It's going to drain back into the muffler further raising the height of that little resevoir.
Reconnected the Anti-siphon and haven't had a problem since.
I did have another unrelated engine cooling water experience recently though. I am travelling this year so LAYLAH is home on the Hard for this Season. While home several weeks ago I was anxious to get her running, I'd only rolled the engine over a few times since haul-out last October.
I would usually place a 5 gallon Pail on the sole, fill it with water and put the intake hose off the thruhull into the pail. Wanting to actually warm the engine up/ let it run for 10 or 15 minutes I elected to connect the garden hose directly to the raw water pump. Hooked things up and climbed down to turn on the water. By the time I was back at the ladder there was already water flowing out the exhaust. Climbed into the cockp[it and hit the starter, Nudding! Assuming I'd flooded a cylinder I pinched off the hose and wedged the Decompression Lever Set in the open position. Rolled her over to clear her, released the Decompression and tried the starter again. Took several tries but she was soon running smoothely.
Lesson here is that the Pump impeller will pass water introduced to it at 45-50 psi!

Anti-siphon sure is safer than memory

The 27' mahogany sloop I used to sail in the summers had a 5 hp Volvo Penta gas engine and no anti-siphon. In place of the anti-siphon there was a valve connected where the anti-siphon was probably supposed to be connected: NEVER FORGET TO OPEN THE VALVE AFTER SHUTTING DOWN !

I almost had nightmares about forgetting to open the valve (or shutting it for that matter as there was only a manual bilge pump) :eek:


-Sven

Not trying to fix anything, really.

The question was raised in another thread about what the water was squirting from one of the transom through hulls. Someone said it wasn't necessary to have the water coming out. Personally I kind of like the water coming out for the reason stated; lets me know the vent is clear and working. (Don't really see a lot of benefit to doing otherwise.) I recalled seeing something in the Calder book about it. He mentioned venting into the cockpit (!). Thought I would test it. After testing I can see that, in my case at least, it won't work.

Someone also mentioned having the anti-siphon loop in the intake line rather than the injection line for the exhaust. I don't see how that would provide any protection at all.

Install Check Valve

Install a Diaphram Type Check Valve. The Anti Siphon is needed only to provide a way to drain your cooling system when the engine stops ! Thats what those little knobs are at the top of the Anti-Siphon that clog up and never work. This is a Vacuum Line that relieves pressure one way.

mherrcat said:

Someone also mentioned having the anti-siphon loop in the intake line rather than the injection line for the exhaust. I don't see how that would provide any protection at all.

Click to expand...

Anti-siphons don't work on the suction side... They close under pressure and open on suction/gravity weight of standing water in the hose. If this is for your engine you really DO need one located between the HX output and the wet exhaust injection point. It should be as high as you can get it and as close to center line as possible..

Water should ALWAYS come out of your wet exhaust thru-hull or you will melt the hoses and have a real mess/problem!!!!

Check Valve in the Vent

The water comming out of your Anti-Siphon is comming out of the Vent connection. The Vent on an Anti-Siphon is a Vacuum Relief. This allows your Cooling System to Drain Down when your Engine has stopped and there is no longer pressure in the hoses. This empties hoses and prevents Siphoning.
The Forespar Anti-Siphons have a Check Valve built in on the top. They don't work very long and leak (waste...yuck!) I remove the rubber valve and pipe the Relief with a Diaphram Check Valve to a hull vent. The VeraLift Site has a great Manual on all of this.....why guess. Go to the Manufacturer ! www.centekindustries.com

Mark
My 85 Ericson 30+ is plumbed exactly as yours is. I like the small amount of water coming out of the antisiphon. It gives me an indication of how much water is going through the exhaust. When the trickle from the anti siphon starts to be a torrent it is time to clean soot out of the water inlet for the exhaust. We have a tendency to just run the engine enough to get the boat clear of the marina and then just sail the rest of the day. Probably are not getting the engine warm enough so we do get some soot collecting in the exhaust. It is much nicer to sail than motor and in Hurricane Gulch there is always an abundance of wind. I do try to run the engine for a longer period occasionally to warm it up good. The recent Isthmus gathering was great for that. I also do not like check valves, if it is mechanical it can and will eventually fail. The system on the 30+ is simple and I like it that way.
Hope this helps
Greg

how much is too much?

Ok... this is an older thread, but my question is along the lines of the original post. So, what is the right amount of water that should be coming out of the anti-siphon vent? Boat is an Ericson built Olson 911S with a Yanmar 2GM20F. Some water comes out the exhaust but it seems like more comes out of the vent in a stream. More water/longer stream as the RPMs increase, engine doesn't seem to overheat even after an 3 hour motor last summer.

I didn't think much about it until another boat owner asked me what the little thru-hull was a couple inches above my exhaust. He was even more baffled when I told him that a stream of water comes out of it when the engine runs. I've only had the boat since the end of the summer and it did this even when we fired the engine up when we first looked at the boat.

If I assume I should have less water coming out, what is the likely culprit? Or better yet, what should I be checking?

Slick470 said:

Ok... this is an older thread, but my question is along the lines of the original post. So, what is the right amount of water that should be coming out of the anti-siphon vent? Boat is an Ericson built Olson 911S with a Yanmar 2GM20F. Some water comes out the exhaust but it seems like more comes out of the vent in a stream. More water/longer stream as the RPMs increase, engine doesn't seem to overheat even after an 3 hour motor last summer.

I didn't think much about it until another boat owner asked me what the little thru-hull was a couple inches above my exhaust. He was even more baffled when I told him that a stream of water comes out of it when the engine runs. I've only had the boat since the end of the summer and it did this even when we fired the engine up when we first looked at the boat.

If I assume I should have less water coming out, what is the likely culprit? Or better yet, what should I be checking?

Click to expand...

I do not know if having a Yanmar makes much difference, but on all the Universals the water feed to the exhaust elbow is T-ed off just before the hose reaches that injection point. From the top hose (looks to be about 1/4") it goes all the way to the transom on our boat and exits via a small thru hull fitting just above the exhaust outlet.
That little syphon break pees out a small stream all the time the diesel is running, a bit more as revs come up. Often there is enough water, at low rpm's, to dribble down from the outlet but not spurt out.

Other builders did not use this simple syphon break, and I have no idea how they deal with the potential problem.
Here is the link to my replacement of the original transom fittings, with some pics.
http://www.ericsonyachts.org/infoexchange/showthread.php?t=7890&referrerid=28

Loren

edit: another anti-syphon thread: http://www.ericsonyachts.org/infoexchange/showthread.php?t=5967

Loren,

I have the same arrangement you do on our 911. At least as far as the transom thru-hull arrangment is concerned. I do not know where it ties into the exhaust side of things though. I haven't looked since the concern popped into my head, but I doubt Ericson would have reinvented the wheel in the couple years between our two builds. I did notice from some pictures of Pacific Boat built 911s and the one 34 that they do not have this arrangement and only have the exhaust exiting the transom.

I'd say that I get about a foot or so of a stream coming out of the vent at idle and more as I increase RPMs. So if yours is right, mine is pretty wrong. Water does still come out of the exhaust, so I know it's not completely plugged up.

I do like the stainless look of yours. May have to convince the Mrs...

Andy

Anti-siphon devices.

All, I have a Yanmar 3GMF fitted with an older version of this Vetus product: http://www.vetus.nl/it/pressrelease...ll&id=1245844834&archive=&start_from=&ucat=7& It doesn't pee at all as the diaphragm valve built into the top of the loop closes immediately when starting the engine. Oh, maybe a drop or two of water comes out of the clear vinyl hose but that's all. In all honesty, I've simply led the vent hose to the top of the bilge adjacent to the engine without any problem since fitting it some 10+ years ago. I could lead it to the now abandoned bronze mushroom fitting next to the exhaust flange but see no point to doing so and would have to fuss with a kluged step-up set of hoses and clamps to accommodate the larger diameter through hull flange. Glyn Judson, E31 hull #55, Marina del Rey CA

Anti-siphon vent hose.

All, I should mention that the clear vinyl vent hose affixed to my Vetus vent is more like an 1/8" one as seen in fish tank air systems as opposed to the larger reinforced vinyl hose depicted in the Vetus link I provided in that last posting, thus the dilemma in attaching it to the mushroom flange. Glyn

I'll have to look at how things are routed next time I'm at the boat. My concern is that I may have a partial blockage downstream of where the vent line starts and it being the path of least resistance is why I get so much water out of it.

It will probably be a week or two before I get back out to the boat though.

Andy

I'd say that I get about a foot or so of a stream coming out of the vent at idle and more as I increase RPMs.

Click to expand...

This seems like a lot of water, at least to me. My Universal M18 only pumps out enough to dribble down the hull at idle. At higher RPM the stream is only about a foot to maybe a foot and a half long.

As someone earlier pointed out, there may be some constriction in the exhaust elbow due to soot or maybe in the larger hoses connected between the heat exchanger/vent loop/exhaust elbow from calcification, but I doubt that. I replaced those hoses when I refurbished my heat exchanger and aside from the hoses being old they did not appear to have any interior restriction.

Also, I have seen drawings of systems where the small 1/4" vent line terminates at the exhaust through hull on the inside of the hull; therefore no separate vent through hull and no water from the transom except from the exhaust through hull.

It may be slightly less than a foot at idle, but much more than dribbling. Next time I'm at the boat I'll trace out the hoses and open up some fittings to see if I can find any blockages or restrictions.

While you are in there looking at the hoses would be a good time to check the heat exchanger zinc, too...

mherrcat said:

While you are in there looking at the hoses would be a good time to check the heat exchanger zinc, too...

Click to expand...

Good point... ah, the joys of boat ownership.

ok... finally remembered to update on this thread... the arrangement I have is a long anti-siphon loop with a t-fitting and a vent hose that then goes to the separate thru-hull above the exhaust fitting.

As far as the "proper" amount of water that should be coming out of the vent, I answered that somewhat on Saturday. The answer is: less than I was having. On Saturday, prior to leaving the slip, while I was checking the flow out the stern, the flow went from "normal" to all out of the vent thru-hull.

My best guess is my exhaust mixing elbow was somewhat blocked and it finished itself off on Saturday. Looks like I will be getting very familiar with the exhaust system on my boat in the next few weeks.