I don’t see a vented loop in the exhaust...a high loop, yes, but not vented...or am I missing something?
Greg
Vented Loop for raw water exhaust.
- Thread starter Scott T-Bird
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Greg
Well, possibly ... but I am referring to the last line that Stu wrote ... "Bill, new to me. Where would that VL be?" This was after Bill wrote "Think we are talking about two different things here. the raw water feed needs a vented loop. Only raw water in that circuit. ... " Stu even quoted Bill's line to be sure what he was referencing.
Go to Post #2 from @sail sfbay and click on the link for "Engine vented loop / Sailboat Owners Forum" to find it directly in the comments.
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You are right ... I think referencing the exhaust is a mistake in this case. It is the raw water discharge hose that is vented. The comments in so many of these threads are really confusing, I think. I think there is generally a lot of confusion over the entire issue. I think that in general, vented loops are used where they are only very rarely needed. With just a little awareness, I think you can live without them. Certainly there are some extreme conditions when a vented loop may save your boat, but I think that most of us never even experience an episode where a vented loop is actually necessary.
Scotty, it appears to me that you really have completely misunderstood my question to Bill in that thread you linked.
What do you mean "Well, possibly...?" The reason I ask is that you brought up my name in this thread and have attributed to me things that I never said or wrote.
"That the last line that Stu wrote ... "Bill, new to me. Where would that VL be?" was me (Stu) referring to BILL'S incorrect comment about a vented loop on the exhaust hose. Go back and read it. Please. You're right, I even included a quote of Bill's statement that I referring to in that post with my question. I did that because vented loops, of course, don't go on the exhaust hose.
Please do not misinterpret or misquote me, and in this case more than once.
Vented loops are very important, and it's critical to understand how & why they are used.
You wrote: "I think there is generally a lot of confusion over the entire issue. I think that in general, vented loops are used where they are only very rarely needed. With just a little awareness, I think you can live without them."
It is important to avoid any confusion on the behalf of others reading this thread, and/or searching this forum for vented loops. You are certainly entitled to your opinion, but these are facts of engineering and hydraulics. In that linked thread I posted for your benefit an entire article about vented loops and exhaust systems. It included diagrams, identical in "design" to the very page of the manual for your own boat that sailsfbay (who doesn't even own a Catalina 320) posted in this thread. I admire him for posting a page of your own boat's manual in this thread which also shows the answer to your question.
The fact that your engine may be destroyed without the proper use of a vented loop should be a good enough reason to understand the correct use and application of these devices. I urge you, as a fellow sailor, to study the issue more. Please. I would also appreciate it if you didn't misquote me repeatedly.
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No, no, no, and NOOOOOOOOOO
!The lack of a vent in your raw water discharge hose (as defined by you in your quotes above) will NEVER, EVER, EVER cause your boat to sink. If the raw water outlet from your heat exchanger discharges to a level BELOW sea level (as shown below), it will destroy your diesel engine with water siphoned into the cylinders. Now on start up, each cylinder will go SLAM, BANG, and POW in rapid succession as the pistons pound down on incompressable water in each cylinder, but it will never sink your boat prior to destroying the engine.
And why will it NEVER, EVER, EVER sink your boat ? Because the intake and exhaust valves in a diesel engine are never open at the same time on any one cylinder. Your diesel, my diesel, anyone's diesel.
Scott, nobody's trying to confuse you here. Everybody else seems to be comfortably in agreement on the subject, namely:
- Watch the discharge level on your raw water hose and depending on its level, USE A VACUUM BREAKER, VENT VALVE, call it what you want but INSTALL ONE IF YOU NEED IT.
- Forget about a A VACUUM BREAKER, VENT VALVE, call it what you want in your wet exhaust hose. That is, unless you are bores and have absolutely nothing to do .
That statement could, on its own, could cause a lot of damage to anyone who happened to believe it.
The high point vent, with siphon break, should be installed on the discharge of the sea water pump, and before the heat exchanger.
When you stop your engine, water can still flow into the open valve on one engine cylinder.
Not to worry about the exhaust, unless you are in heavy seas and the muffler water sloshes backwards.
That siphon break is needed, if your fresh water pumps bypasses or is worn.
Jim...
PS: Water pump pressure closes the siphon break valve, then opens when no pump pressure.
When you stop your engine, water can still flow into the open valve on one engine cylinder.
Not to worry about the exhaust, unless you are in heavy seas and the muffler water sloshes backwards.
That siphon break is needed, if your fresh water pumps bypasses or is worn.
Jim...
PS: Water pump pressure closes the siphon break valve, then opens when no pump pressure.
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@Stu Jackson , I never intended to misquote you. That is why I cut and paste the quotes from Bill and you in that 2014 thread verbatim. To be fair, I did say that I may have misinterpreted your quote. As it turns out, I think that I could have been misled by your response. You, yourself, quoted Bill's reference to the vented loop in the "raw water feed" but it was followed by the ... and you didn't include the rest of the quote that referenced a vented loop in the exhaust hose. Then you responded as I quoted you. So I did not misquote you. I simply didn't realize that you were referencing the exhaust hose instead of the raw water feed. I apologize for not following your train of thought, and I can see it now. But I did not misquote you. I used the exact sequence of references (cut and paste) that were included in the 2014 post. Read thru that thread very carefully and you will understand the reason that I misinterpreted your intention. You have a way of making some shorthand references that can lead to confusion.
I'm pretty sure it is between the heat exchanger and the mixing elbow.
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Just to be clear, I did not say that the lack of a anti-siphon break in the raw water hose could sink the boat. I said that having one could save your boat in an extreme situation. Ok, it could save your engine ... mea culpa. I normally wouldn't find it necessary to defend this minor point, but your histrionics seemed to warrant it.No, no, no, and NOOOOOOOOOO
The lack of a vent in your raw water discharge hose (as defined by you in your quotes above) will NEVER, EVER, EVER cause your boat to sink. If the raw water outlet from your heat exchanger discharges to a level BELOW sea level (as shown below), it will destroy your diesel engine with water siphoned into the cylinders. Now on start up, each cylinder will go SLAM, BANG, and POW in rapid succession as the pistons pound down on incompressable water in each cylinder, but it will never sink your boat prior to destroying the engine.
View attachment 193687
And why will it NEVER, EVER, EVER sink your boat ? Because the intake and exhaust valves in a diesel engine are never open at the same time on any one cylinder. Your diesel, my diesel, anyone's diesel.
Scott, nobody's trying to confuse you here. Everybody else seems to be comfortably in agreement on the subject, namely:
- Watch the discharge level on your raw water hose and depending on its level, USE A VACUUM BREAKER, VENT VALVE, call it what you want but INSTALL ONE IF YOU NEED IT.
- Forget about a A VACUUM BREAKER, VENT VALVE, call it what you want in your wet exhaust hose. That is, unless you are bores and have absolutely nothing to do .
That statement could, on its own, could cause a lot of damage to anyone who happened to believe it.
If you need my definition for the point of discharge for the raw water hose (after the anti-siphon break), I define it as the joint at the mixing elbow, which is definitely well above water level. You seem to be relying on the hand-drawn sketch in the manual for your information. You should realize that it is just a schematic and it really does fail to show the origin and termination of the raw water hose. It only accurately portrays the location of the anti-siphon vent. Here are the actual connections:
The raw water pump feeds HE in a direct feed. (Just to show how confusing all the commentary can be, @JamesG161 seemed to indicate that the anti-siphon should be between the pump and the HE.) After circulating thru the HE, the hose exits the top and winds 11' over to the port lazerette before returning another 11' back to the mixing elbow. Both connections are well above water line, contrary to the poor schematic that seems not able to define the ends of the hose. Of course, it would be a closed system all the way from the sea water thru hull to the mixing elbow and there could be the potential for a siphon, I suppose, if the boat were heeling to such a great extent that the mixing elbow was below seawater level, but I really believe this could only be a very rare occasion.
So, the cost of the hose and anti-siphon (I'm installing new) is a little less than $200. The labor is a little intensive, given the location of the vent. Yanmar says that you only need about a 12" length of hose to make the direct connection. I concede against common sense and will install the anti-siphon.
Perhaps I didn't need to open this thread. I certainly know how a siphon works and I know when an anti-siphon vent is absolutely needed. Many of these devices are installed, it seems, as a precaution against certain rare occurrences. Certainly, many folks have testified that they don't have one in this circumstance and they never knew they needed one. I'll give you a hint ... they don't, necessarily. I asked the question to find out if there are any clear answers. It turns out that there really aren't. It seems that there are just a lot of strong opinions and most seem to be completely impervious to actual science and to nuance.
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Here is what it looks like on the H-34 .. same engine configuration.. Vented loop is between the heatex and the exhaust ell injection.. It is slightly lower than the top of the big loop (not vented) in the exhaust hose after the muffler and before the thru-hull..
Good grief man. There is only one person who is impervious to science and that's YOU. I really don't think you've learned one thing from this entire discussion. It always turns out to be everyone else who is wrong and you're always right.
Closed system ? ? ? ? ? Do you even know the difference between an open system and a closed system ?
I rest my case. I quit.
Well, maybe I don't. I'm thinking there is no air introduced from the thru hull, strainer, seawater pump, heat exchanger until the joint at the mixing elbow, with all the hoses in between (except for the anti-siphon vent). So, what I actually meant is that it is closed thru to the elbow if there isn't a vent. If I'm missing something, then please let me know.
I'm not actually even arguing anything. I'm replacing the original in exactly the same fashion despite my opinion that it isn't absolutely necessary. I'll readily admit that the boat designers know far more about it than I do, so I'm not about to change it.
I'm also suggesting that the variety of answers are off the wall - all you have to do is read all of the responses that have been presented now and in the past. A lot of people just fire off responses that are just misinformation, and perhaps I do as well. At least I'm willing to mine in on any issue that I might be mistaken about. Even you suggest that the hose clearly discharges below water level (based on your interpretation of a hand-drawn schematic). It clearly discharges above the waterline, and that is what I described in my original post. So, you seem to be arguing over a false assumption. So be it. I'm done as well.
That was ideal spot, but your HE is more accessible than a few engines.
The siphon break is needed, even if it is down stream of the HE.
Here is the kicker...
That siphon break valve is pressure to close, thus more pressure nearer to the pump.
You need to maintain that valve too. So it must be a spot easily accessed.
I guess, if you see a leak on that valve [engine running], you might be seeing a restriction on the HE, or wearing water pump.
Down stream of HE is ok.
Jim...
PS: The height of the siphon break is not critical , as long as it is above the engine and boat water line.
If the entire exhaust system and cooling water system is above the waterline, a vented loop is not necessary. If any of it is below the waterline a vented loop is necessary. Here's what Vetus says about their mufflers.
Wide collection Boat Exhaust systems at VETUS boat parts
VETUS is an internationally operating developer, manufacturer and trading company, selling marine engines, generators and technical equipment for recreational craft and small commercial vessels.www.vetus.com
So I just read what Vetus has to say about it and I looked at their diagrams .... here is their quote.
Installation above or under the waterline?
The cooling water injection point is crucial. If the water injection point is 15 cm or more above the waterline, the cooling water can be injected directly into the exhaust system. But when it is less than 15 cm above or even below the waterline, the cooling system can siphon water through the intake when the engine is turned off. Water can fill up the exhaust system and get back into the engine through the exhaust valves.
They don't seem to say "If any of it is below the waterline a vented loop is necessary." Instead they say that if the injection point is below the water line (or within 15 cm - 6") then a anti-siphon vent is necessary. They specifically say that if the injection point is above 15 cm, then the cooling water can be injected directly. The run from the heat exchange to the injection point (mixing elbow) is at least 6" above the waterline.
I will readily concede that a heeling sailboat makes that whole water line issue a gray area and just to be safe, I go along with the anti-siphon vent.
Thanks, I know that you think like an engineer (and are one, tooThat was ideal spot, but your HE is more accessible than a few engines.
The siphon break is needed, even if it is down stream of the HE.
Here is the kicker...
That siphon break valve is pressure to close, thus more pressure nearer to the pump.
You need to maintain that valve too. So it must be a spot easily accessed.
I guess, if you see a leak on that valve [engine running], you might be seeing a restriction on the HE, or wearing water pump.
Down stream of HE is ok.
Jim...
PS: The height of the siphon break is not critical , as long as it is above the engine and boat water line.
), hence the explanation. Where Catalina put the vent is not so easy to get to. If I didn't have an air condition system, it would be a little easier to get at thru the lazerette. As it was, I had to crawl halfway in through a galley cabinet that had to be removed! 
Thanks Scott for posting that. That is the key part for me to understand the issue. I was trying to figure out where the water would be coming from that the vent was intended to prevent. Sucking water up from the exhaust side doesn’t make sense, because like Scott said in the first place the elbow starts with air in it, but up the intake could happen. For this situation the height of the exhaust outlet in the transom and muffler make no difference, only the height of the outlet of the raw water injection into the manifold.
Having said that, sucking water up the intake can only happen if the impeller is missing one or more vanes (depending on pump geometry), and if the impeller stops at just the right place for those missing vanes to allow flow from input to output.
It would take less than that. An impeller that does not make a good seal for any reason would allow water to bypass the the pump and siphon out.