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Old 07-01-2016, 07:42 PM   #1
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Wet exhaust lift

What am I missing?
These pictures are a Perkins' in a 49 De Fever, stand up ER.
The mufflers must be at least 4 feet below the waterline.
I can't grasp how the water in the exhaust can travel up that distance and out.
Or, how the water does not back into the exhaust.
Tom?
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Old 07-01-2016, 09:49 PM   #2
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Good question and spot on observation.

On my similar, if not identical setup to what is pictured, the amount of water remaining in the exhaust run drain back is pretty small. I know this because on several occasions I have inspected the internals of the water lift.

Inside the water lift was about 2 cups of carbon (after about 1500 hours) and maybe six inches of water. Say maybe 1 1/2 gallons or so. This is pretty common for water lifts. With the 5 inch exhaust tube about 1/2 full of water for the roughly 3 foot tube column that seems to equate. Obviously the water lift has to be sized to sensibly accommodate the drain back volume.

One difference, our vessel has a siphon break on each exhaust due to low engine placement in relation to waterline. Not unlike thousands of sailboat setups.
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Old 07-01-2016, 09:59 PM   #3
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The height of the lift accomplishes two things, the higher the lift, the quieter the exhaust (without exceeding backpressure limits) and the high rise helps prevent backflooding.

Sunchaser is spot on about sizing, not as critical with propulsion engines because they are usually pretty big because they have to be, but on generator systems with separators properly sized lifts to accommodate the water in the lift pipe at shutdown is crucial. Some gen lifts are tiny, and can become full pretty easily.




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Good question and spot on observation.

Obviously the water lift has to be sized to sensibly accommodate the drain back volume.
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Old 07-01-2016, 10:15 PM   #4
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I guess I'm hung up on volume. My head tells me if the hose was disconnected from the exhaust elbow, ahead of the muffler, it would fill a bucket pretty quick. So I visualize that water going into the lift muffler and wonder how it can climb that hill. Or is it mostly vapour?
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Old 07-02-2016, 12:11 AM   #5
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About 1.5 - 2 psi of exhaust pressure is used to move water uphill and out of the vessels exhaust.


Maybe towards the end of July we could take some recliners into our ER, sip a beverage and talk over this puzzler. Bottom line, size the lift muffler to take drainage water from hoses and be no more than say 1/3 full upon shutdown. Looks like DeFever did it just fine.
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Old 07-02-2016, 12:36 AM   #6
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About 1.5 - 2 psi of exhaust pressure is used to move water uphill and out of the vessels exhaust.


Maybe towards the end of July we could take some recliners into our ER, sip a beverage and talk over this puzzler. Bottom line, size the lift muffler to take drainage water from hoses and be no more than say 1/3 full upon shutdown. Looks like DeFever did it just fine.
Now that sounds like a plan, I'll remember to bring my own pool cue this time.
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Old 07-02-2016, 09:16 AM   #7
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Another fact to consider. A column of water generates 0.4 psi per foot of height, so 2 psi of exhaust pressure can push a 5 foot water column.
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Old 07-02-2016, 09:30 AM   #8
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Not to mention that boat only draws between 4-5' of water I would think. So I doubt the mufflers are 4' below the water line.
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Old 07-02-2016, 10:47 AM   #9
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Not to mention that boat only draws between 4-5' of water I would think. So I doubt the mufflers are 4' below the water line.
On my vessel the water column height is measured from the entrance to the water lift to the exhaust hose spill over point - about 3 1/2 feet add a potential stern sea of say 3 feet and easy to see a pressure design factor of 6 or 7'.

It would interesting to know Centek's test pressures.
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Old 07-02-2016, 10:53 AM   #10
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On a good water lift muffler system about the only noise the exhaust makes is the sound of the exhaust water falling.

I would think a larger muffler diameter might lower the exhaust pressure required to get the water up and our.

The largest danger with a small muffler volume is a no start situation ,

where the engine is cranked to prime and the exhaust continues to fill with water , until reaching a cylinder.

A drain to winterize can be used to empty the muffler if much engine cranking is required.
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Old 07-02-2016, 11:11 AM   #11
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Quote:
Originally Posted by FF;
I would think a larger muffler diameter might lower the exhaust pressure required to get the water up and out.
That is what got me thinking. Small hose into a large canister with a larger hose out and up.

I'm sure though, if I go camp out in sunchasers ER, he will easily show me how 3 stick men can be chased up a hill by one.
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Old 07-02-2016, 11:16 AM   #12
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Originally Posted by sunchaser View Post
On my vessel the water column height is measured from the entrance to the water lift to the exhaust hose spill over point - about 3 1/2 feet add a potential stern sea of say 3 feet and easy to see a pressure design factor of 6 or 7'.

It would interesting to know Centek's test pressures.
You read my mind and that isn't always easy as the old grey matter is covered in green stuff.
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Old 07-02-2016, 11:33 AM   #13
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In addition to the rise of exhaust in the engine room that you have shown; if the exhaust hose can not pitch down to the transom and emerge above the waterline, then a "gooseneck" should be incorporated at the transom usually another 12"-18" of lift. This so that anchored in a seaway, the pitching does not roll water down the hose run, filling the waterlift muffler little by little, finally flooding the engine.
Of course a savy operator could open the muffler drain when anchored in the trades allowing the water to run to the bilge and be pumped out.
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Old 07-02-2016, 01:57 PM   #14
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It's amazing the boat/engines have lasted so long with all the flaws in the exhaust system.
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Old 07-03-2016, 06:45 AM   #15
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Having the engine exhaust open 100% of the time to a cylinder of water does seem strange.

But it seems to work, with care.
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Old 07-03-2016, 07:11 AM   #16
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Having the engine exhaust open 100% of the time to a cylinder of water does seem strange.
Elementary my dear FF. Wet exhaust design 101.
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Old 07-03-2016, 07:16 AM   #17
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As a reference tool: the volume of water in a pipe or hose is .785 X Dia. (in feet)squared X 7.48. per foot of pipe in gals. So in a 4" hose it is .785 X .333 X .333 X 7.48 = .61 gallons. It certainly depends a lot on the temperature of the exhaust gasses as to how much of this volume turns to vapor during the cooling and discharge process, but I would imagine a significant portion.
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Old 07-03-2016, 07:22 AM   #18
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The water gets "splashed" up hill as a pretty turbulent exhaust/water mix. It does not need to be as much pressure as it would take to force the water uphill should the hose be full of water. One way to look at it is I can spit four feet up in the air, but have a hard time blowing 48" on a water manometer.
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Old 07-03-2016, 07:40 AM   #19
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Further to Ulysses and Ski's points, water lift muffler sizing is based upon a shutdown situation with the the real non gaseous volume of solution safely stored to prevent an engine flooding situation.

But as FF noted several posts ago, too many cranking events with a no start and open sea cock can flood some wet exhaust designs.
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Old 07-03-2016, 10:44 AM   #20
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This thread and it's traction surprises me.
In an ok way.
When I posted, I thought it would get two replies both ending with the word "dummy."
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