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Old 25-03-2008, 20:20   #16
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I agree with Paul, I would not use anything other than bronze sea strainers. My Groco's have been in service for over twenty years now and the only thing I have had to do is replace the filter itself and the seals. Their condition essentially makes them still brand new. I think the additional money is good insurance against sinking.
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Old 25-03-2008, 23:10   #17
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Originally Posted by Pblais View Post
I'm not sure how this has anything to to do with this thread. If I figure out how I will let you know.
Perhaps I can help? Maybe it is something to do with someone who, among others, appears to have no understanding whatsoever of reinforced plastics introducing their wide sweeping claim that plastic strainers are not suitable below the waterline. Which is kinda silly when one considers boats are most frequently made from them.

Of course, if others are not allowed to respond to such absurd claims please tell us and we will go elsewhere.
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Old 26-03-2008, 14:42   #18
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I currently believe the only disadvantage in locating the strainer below the waterline, is spillage (when you need to open the strainer, you close the seacock, but back flow from the heat exchanger and engine may spill). To stop the back flow, I plan to install a manual valve just upstream of the strainer.
Martin, I wanted to check for sure on our boat how ours was done before reciting one way that backflow can be minimised by considering the static hydraulics when routing the hoses, etc as I mentioned earlier. I have now done so -

As said the strainer is below the waterline - then the hose to the water pump">raw water pump suction is laid in the bilge below the level of the top of the strainer. It then rises close to vertical up to the pump. The discharge side of the pump goes into an anti siphon loop which isolates everything beyond that (heat exchanger, etc) from the strainer in the static situation so one ends up with the only back flow being from the difference of the static water level in the rise of the pump suction hose and the top of the strainer (assuming the strainer is full to the top which is the worst case).

The anti siphon loop is the usual one fitted to stop siphoning of raw water through the engine when the engine is stopped and the raw water seacock is open (and possibly damaging the engine). Traditionally this loop is located on the exhaust side of the raw water flow over where the raw water is injected into the exhaust gases from the engine. However, I know of no reason as to why it should have to be there and as I say ours (and others) is on the raw water pump side - maybe yours could be arranged the same.

There is another advantage of doing it the way I describe if that is possible - when the antisiphon loop is installed on the exhaust end of the raw water flow the valve on the top of the loop is subjected to the exhaust gas pulsations and can lead to the common problem of them dribbling water. This is not a problem if the loop is able to be fitted after the raw water pump instead.

We used the Marelon strainers on our own boat (for sea water services as well as for the engine), mainly because they are very squat so easily fit under the cabin sole with room under them to hold a shallow container to catch any drips. We have had no problem with them apart from the corrosion of the stainless steel strainer baskets which we fixed by epoxy coating the welds as I mentioned earlier. Obviously :-), a quality metal strainer of a proven brand is also fine (the metal we normally go for on new builds is stainless steel but I suspect these may be more expensive than bronze).

John
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Old 26-03-2008, 17:40   #19
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Like I said before...the bronze one's are a much safer bet and allow me to sleep at night.
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Old 26-03-2008, 20:49   #20
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Waterline, strainer and Anti-siphon

John, your detailed thoughts on and description for minimising back flow are much appreciated. I will skip the proposed upstream valve and, expecting minimal back flow, will just handle it with a rag or little pan under the strainer. And get a better built strainer.

Regarding the location of the anti-siphon valve, I know it is not strictly the topic of this thread, but I am quite interested in that as well. I take it your installation is:

Strainer => Pump => Anti-siphon => Heat exchanger => Exhaust elbow.

If so, then you are saying that, even if the anti-siphon valve is behind the heat exchanger, it will still suppress potential siphoning of water from Water Lock to Exhaust Manifold. That will certainly give me more options as to where to install the anti-siphon loop and valve.

But may I just ask the following: If the engine is not running, and the heat exchanger is filled with water, would that not cut off the anti-siphon valve's air path to the exhaust injection point?

Or is it a pre-requisite for your installation that the heat exchanger be elevated above the injection point, so that it partially (or fully?) drains when the engine is shut off, ensuring an air path to the injection point?
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Old 26-03-2008, 23:34   #21
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Originally Posted by sildene View Post
Regarding the location of the anti-siphon valve, I know it is not strictly the topic of this thread, but I am quite interested in that as well. I take it your installation is:

Strainer => Pump => Anti-siphon => Heat exchanger => Exhaust elbow.

If so, then you are saying that, even if the anti-siphon valve is behind the heat exchanger, it will still suppress potential siphoning of water from Water Lock to Exhaust Manifold. That will certainly give me more options as to where to install the anti-siphon loop and valve.
Yes it will stop siphoning but the antisiphon loop is to prevent siphoning from the raw water inlet seacock through the engine's raw water circuit to the raw water injection point into the exhaust system. It is nothing to do with siphoning back from the waterlock muffler which should be impossible if the muffler is correctly located.

If this potential inlet seacock to exhaust siphon is not broken then seawater can siphon over that path, fill the water lift muffer and back up into the engine through the exhaust valves.

Downstream of the water lift muffler in the exhaust pipework towards the discharge to the sea there should be a loop upwards well above any waterline to stop seas pushing back up into the muffler and flooding it back up into the engine. This loop means that if a siphon starts from the raw water inlet seacock through the engine to the water lift muffler it will flood the waterlift muffler and then back up into the engine through its exhaust valves.

Or should there be no waterlift muffler the exhaust pipework between the engine and the loop (the one stopping seas pushing back up the exhaust, not the antisiphon one) will similarly, but much more quickly, flood backing up into the engine through its exhaust valves.

Quote:
Originally Posted by sildene View Post
But may I just ask the following: If the engine is not running, and the heat exchanger is filled with water, would that not cut off the anti-siphon valve's air path to the exhaust injection point?
The antisiphon valve does not need an air path to anywhere except to the top of the antisiphon loop. When the engine stops running so the water settles to the static situation then the side of the loop that the pump is in will drain down to the level of the boat's waterline. The other side of the loop will drain down depending on the configuration of the pipework and heat exchanger from then on - the draining from that side will be from hoses and exchanger (maybe, according to its elevation) into the water lift muffler. The volume that drains down into the muffler would normally be quite small - in our own case can hear it running into the muffler for a second or two. As long as the top of the anti siphon loop has air in it then there can be no siphon regardles of the upstream and downstream situation.

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Originally Posted by sildene View Post
Or is it a pre-requisite for your installation that the heat exchanger be elevated above the injection point, so that it partially (or fully?) drains when the engine is shut off, ensuring an air path to the injection point?
No, the heat exchanger does not need to drain. As above all we are aiming for in the antisiphon loop is to break any possibility of siphoning occurring between the inlet seacock and the raw water injection into the exhaust. That just needs air in the top of the antisiphon loop which will come in via the valve at the top of the loop (some people don't use a valve but run a small diameter hose to overboard, but as I said before that should not be necessary if the anti siphon loop is not at the exhaust side of the engine - the valves normally leak due to sensitivity to the exhaust pulsations).

Just keep in mind that whatever you do has to fully consider the layout of your engine and associated pipework as the above is only a potential guide - there may be something important we do not know or have misunderstood about your arrangement. If it is a new engine one should get the engine supplier to validate the arrangement.

Has taken some metal gymnastics to try and write that and no doubt will need some to read it. Think I have it all flowing correctly (with no leaks ) but if I have made a Boo Boo maybe someone with solid engine installation experience could point that out.
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Old 27-03-2008, 04:07   #22
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See also the Northern Lights tutorial:
Please Don't Drown Me
A guide to installing smaller Northern Lights generators
http://northern-lights.bz/PDFs/misc_...t_drown_me.pdf
~ or ~
http://www.coastalmarineengine.com/m...t_Drown_Me.pdf
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Old 27-03-2008, 14:45   #23
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To the rescue again with a nice link . The first diagram shows it exactly.

The only thing I would add is that if a side discharge exhaust on a sailboat one has to keep the minimum height of the exhaust from the waterlift muffler to the discharge out the side of the boat well above the heeled (including knocked down) waterline - the 1 foot mentioned would seem more appropriate to a power boat and insufficient for a sailboat to me. The 1 foot mentioned would also seem too little to me for a transom discharge with biggish following seas (ours is in the order of 1 metre).

Of course the engine has to be known to be capable of pushing the water/exhaust up such lifts (the lift being from the waterlift muffler to the highest point between it and the discharge overboard) and the waterlift muffler have adequate capacity to take all drain back when the engine is stopped.
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Old 27-03-2008, 14:57   #24
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Quote:
Originally Posted by GordMay View Post
See also the Northern Lights tutorial:
Please Don't Drown Me
A guide to installing smaller Northern Lights generators
http://northern-lights.bz/PDFs/misc_...t_drown_me.pdf
~ or ~
http://www.coastalmarineengine.com/m...t_Drown_Me.pdf

Thank you so much for the pictures.

I can't see it in words.

Picures make it so simple for me.

How often does one clean the anti siphon thingy?
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Old 27-03-2008, 17:33   #25
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As they say, a picture is worth a thousand words .

I had a quick hunt for one showing the anti siphon loop just after the raw water pump and couldn't find one .
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Old 27-03-2008, 19:35   #26
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Thank you John, Gord for the clarification on anti-siphon valve placement.

MidLandOne said:
Quote:
Of course the engine has to be known to be capable of pushing the water/exhaust up such lifts (the lift being from the waterlift muffler to the highest point between it and the discharge overboard) and the waterlift muffler have adequate capacity to take all drain back when the engine is stopped.
Regarding calculation of capacity of the waterlift muffler to handle drain back, bar talk suggested it be 20% of the internal volume of the exhaust line, from muffler to exit. Can anyone confirm this?

The factors to consider here may include:
  1. In rough conditions, the stern may be up when you shut the engine, so, despite a slight fall in the line towards the stern exit, you may have to assume that all the water in the line at the time may drain towards the muffler.
  2. The exhaust hose would never be 100% full with water - only pulses of water; so what maximum volume can we assume the pulses to occupy, in percentage terms?
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Old 28-03-2008, 15:36   #27
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Regarding calculation of capacity of the waterlift muffler to handle drain back, bar talk suggested it be 20% of the internal volume of the exhaust line, from muffler to exit. Can anyone confirm this?
That would seem, at a guess, reasonable to me. Some engines pump a lot more water than others though.

My suggestion would be to compare the volume of whatever muffler you intend using with a Centek one of similar style for the same diameter exhaust as yours (Centek Industries) - they make them down to 40mm I think, so I am assuming your exhaust is at least 40mm. I would have a high level of confidence that the volumes of the Centek ones are adequate taking into account all likely draindowns and also including some headroom for water pumped through the engine when cranking (and cranking, and cranking a few times more if a starting problem).

If you can spring to a Centek muffler cash wise then I would recommend them. I have no experience of my own with Vetus mufflers but I have had quite a number of first hand reports (from the owners themselves) of them melting when they have lost cooling water due to a pump impellor failure (or forgetting the raw water seacock ) so filling the boat with exhaust fumes.
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Old 17-02-2010, 16:06   #28
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I also have the the Vetus 150 going on 18 years. It was installed per manufactures instructions. My problem now is sourcing replacement o-rings, one small, one large. The 150 is now out of production and supply lines have slowed in these slow economic boat times. I'm just about to cut my losses and buy a new Vetus 330 just because it's a bolt in replacement.
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Old 17-02-2010, 20:39   #29
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I know the strainer that Paul talks about... they stopped selling that many many years ago ;-) Forespar had an identical one. The new ones are grey plastic with a transparent lid that screws on top like a jar so not the center rod and wing nut on top. I think they would do okay under the water line but, if you have the choice, why not choose the optimal position: right at the waterline so that both inlet and outlet are flooded but the lid is well above. I did that a couple of years ago and really love it. Here's why: when cleaning it, I leave the seacock open and back-flush it with a hose. Some scraping and scrubbing and more backflushing. All that nasty stuff goes out the way it came in instead of me taking it out and away. Neat!

cheers,
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