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Old 10-30-2018, 05:44 AM   #1
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What is this? Wet exhaust outlet

So I have a 2.5 inch valve and the water flow out of it is very low.

Upon removing the Pipework I can see the following, but I’m unsure if it’s anflow restrictor?

It’s on the through hull valve for the wet exhaust outlet of the exhaust system.

The design of our system have two outlets overboard. One pumps well, the other ( this one) seems to trickle, whereas the port side both outlets flow about the same.

https://imgur.com/2YSUT0l

A very small amount of water moves through the opening at the bottom of that valve.
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Old 10-30-2018, 06:29 AM   #2
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Is that a buildup of corrosion product or mineral deposit? Can it be chipped out? What is the flowpath here?
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Old 10-30-2018, 06:33 AM   #3
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That is the through hull fitting to offboard the seawater from the wet exhaust.

When viewed it looks like a purposely installed restrictor. My questions is whether I’m right and if it needs to exist as it’s only one one side. I’m guessing it might have been installed at some stage to solve an issue I’m in aware of.
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Old 10-30-2018, 06:46 AM   #4
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Looks like a valve in series, why would a restrictor be installed when valve position could be changed?

And it makes no sense that a small diameter line would be installed off the wet exhaust, that is why a request was made describing flow path. In detail.
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Old 10-31-2018, 01:26 AM   #5
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Looks like the ball valve is only partially opened.
You should see a full moon in there when the handle position is inline with flow.
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Old 10-31-2018, 03:15 AM   #6
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Ok, Thanks for that, I will take another look and report back.
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Old 10-31-2018, 05:19 AM   #7
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If this is a typical wet exhaust and the gas and water discharge together, there is no reason to restrict flow, and restricting exhaust gas flow can cause excessive backpressure.

Any restriction in a system like this is counterproductive, the entire system should be designed to allow gas and water to discharge with as little restriction as possible.

If your exhaust system discharges gas and water separately there is no reason to restrict waterflow on the drain line. Once the water has done its job the idea is to discharge it ASAP.

One possibility may be that the impeller may be damaged or worn or some other component of the water intake system (strainer, heat exchanger, etc.) may have a restriction in it.

Would be helpful if you could describe the exhaust system.

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Old 10-31-2018, 05:35 AM   #8
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The wet exhaust injects seawater ex heat exchanger into the exhuast flow after the turbo which settles into a muffler. The seawater from that can then drain from that muffler out the side of the hull through the aft water outlet.

The muffler is then piped to a second muffler box above the water line which continues up through the top of the boat ( the exhuast stack ). This pipe drains that second muffler box and the water that collects there.

These are 19 liter Cummins kt19ís.

Iíve attached some pics to try and provide an idea of how itís setup but itís difficult to photograph.
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Old 10-31-2018, 06:05 AM   #9
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Sounds like quite a hybrid of a system. Can't tell much from the photos, but from the photos and your description my take is this:

Dry exhaust from turbo goes into insulated hump. Water from HX is injected at bottom of hump, then mixed flow goes into lower muffler. That has a drain that goes overboard. Wet (but less wet) exhaust goes upward to second muffler, which also has a drain overboard. Cooled but damp exhaust then goes upward to stack at top of boat. If too much water exists at exit, messy water spews on the deck.

If my understanding is correct, the restricted fitting is the drain for one of the mufflers. I would see no benefit to that restriction, as all it will do is reduce the draining of the muffler which is not desirable.

I'd consider removing the restriction. It has a valve in series, correct? If you want to limit flow you could use the valve??
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Old 10-31-2018, 10:31 AM   #10
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I had similar setup on a 1995 Tolly 45 I owned years ago. Part of the raw water flow before the mixer was redirected overboard through a gate valve. It was explained to me that the gate valve was set at the factory to "balance" raw water flow through exhaust. It was nice to immediately see the raw water flow when starting up the engine but it seemed like an unnecessary complication.
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Old 10-31-2018, 11:28 AM   #11
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The valve may be an exhaust bypass valve to send it straight out rather than through the mufflers?
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Old 10-31-2018, 11:44 AM   #12
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Curse of the Kiwi/US time zones!!

One further question based on my above post, I wonder if there is any heating problems in the two mufflers, and maybe they wanted less flow from a drain to keep muffler temps down. Might check the other engine that seems to be free flowing.
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Old 11-01-2018, 05:14 AM   #13
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Quote:
Originally Posted by gsholz View Post
I had similar setup on a 1995 Tolly 45 I owned years ago. Part of the raw water flow before the mixer was redirected overboard through a gate valve. It was explained to me that the gate valve was set at the factory to "balance" raw water flow through exhaust. It was nice to immediately see the raw water flow when starting up the engine but it seemed like an unnecessary complication.
This pipe exits from the smoke stack muffler box. So - well after the mixer, muffler and before the smoke stack exits the top of the boat.
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Old 11-01-2018, 06:11 AM   #14
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I believe you are right on Ski, a muffler designed to drain is supposed to drain, and any restriction is just counterproductive.

It still might be worthwhile to make sure the water flow reduction is not being caused by a restriction upstream, strainer, impeller, thru hull, etc.

And excellent suggestion about temps on the components. Many boats use a infrared temp "gun" and "shoot" various spots on the exhaust system. Its a good idea to mark these spots so the same spot in measured for accurate comparisons. On some vessels I have seen dates/temps/rpm noted on the piece of tape marking the spot as a running record. This can give early indication of any issues. Here in the US Harbor Freight has them for about $30

Quote:
Originally Posted by Ski in NC View Post

If my understanding is correct, the restricted fitting is the drain for one of the mufflers. I would see no benefit to that restriction, as all it will do is reduce the draining of the muffler which is not desirable.

I'd consider removing the restriction. It has a valve in series, correct? If you want to limit flow you could use the valve??

This is more common on generator systems, the "raw water bypass." Some engines pump much more water than a wet exhaust system needs or can tolerate and the excessive water creates over spec backpressure. Typically a tech will install a gate valve into a T in the raw water line just before the mixer / spray ring and divert some water to someplace after the exhaust system or overboard. The Tech will set the valve while watching back pressure and temps at full load and when the right setting is found the handle is removed, ty rapped or labeled so someone with OCD doesn't open or close it.

Don't ask how I know



Quote:
Originally Posted by gsholz View Post
Part of the raw water flow before the mixer was redirected overboard through a gate valve. It was explained to me that the gate valve was set at the factory to "balance" raw water flow through exhaust. It was nice to immediately see the raw water flow when starting up the engine but it seemed like an unnecessary complication.
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Old 11-02-2018, 02:59 PM   #15
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Wet mufflers often divert some of the exhaust water. Especially in bigger engines. Too much water in the muffler causes too much back pressure, hurting economy. Depending on temps, it's better to have too little water rather than too much. The two engines could have different settings because of a past problem, now gone, or the result of someone fooling with a system they knew nothing about.

The amount of diverted water is not set in stone. Changes need to be made because of changes in the impeller, age of the engine, water temperature, and buildups it the sea water plumbing that can't be addressed while underweigh.
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Old 11-04-2018, 06:04 PM   #16
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I spoke to the previous owner who I was hoping would shed some light on the issue.

He couldn't understand why it was locked closed the was it was, other than that the valve may have seized part closed. So with this knowledge and the understanding that it should be fully open, I am going to attempt to free the blocked valve. Second-hand valves were used as they were "available" at the time. I'll check to see whether there is a replacement option available to me. It's evident these pipes have not ever been dismantled - so probably timely.

I'll try and take some better photos / and document progress as a matter of interest for those following

Thanks for the comments and discussion thus far trawler people. Appreciated.
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