Muffler Net Volume.

[John, CD28]

I've got a new Naqualift muffler with a side angle in, and top out. The cylinder (body) is 6.5" high, and about 6.5" in diameter. It's pretty small to begin with, but that's all I have room for. Based on this, I calculated (pi x radius^2 x height) the volume of the muffler (thinking water holding capacity) to about 215 cubic inches, or just short of 1 gallon (231 inches). That would be fine.

Now, when I look at the angle inlet tube into the muffler, I see it reaches to within about 2" of the bottom of the cylinder. I don't see any vent inside there, or anywhere in/on the muffler. I'm concerned upper area of the muffler will be just a trapped air bubble, effectively reducing the volume of water the muffler can hold before it starts sending water up to the exhaust manifold. If the effective net area is only 2" high, instead of 6.5" the water holding capacity is reduced to just 66 cubic inches, or about a quart, meaning 3/4 of this muffler will always be full of air/exhaust gas that can't get out, and not available as water holding capacity.

Based on this, I got a measuring cup and started pouring water into the outlet side of the muffler. It started to overflow and come out the inlet side at 36oz, far less than the 128oz (1 gallon) range I'd hoped for.

I've gone ahead and drilled a small hole through the inlet tube wall just inside the body of the muffler to form a passage/vent from the highest internal part of the inlet tube. This will relieve air pressure of the bubble to the height of that point into the inlet hose side, raising the water level inside the muffler, but it still looks like the top half, or third, of this muffler will be full of trapped air/exhaust.

Does anyone know if there is something in these mufflers (Vernalift or Naqualift with angle in) to prevent the upper section of the muffler from trapping air that displaces water?

All input much appreciated,
John

[John, CD28]

After drilling the vent hole, and letting the epoxy cure in the hole I had to drill in the lower half of the tube to allow the bit to reach the upper inside of the tube, I repeated the water volume test.

With the new vent hole, the muffler now holds 54oz of water before it starts to overflow the inlet side, much better than the 36 oz before I drilled the hole.

Do the top in, top out, mufflers trap air in them?

John

[bcooke]

I guess I am not sure why you are worried about it in the first place. Is there something wrong with the unit as designed? It should work straight out of the box with no modifications. Why is the volume of the muffler a consideration in this case?

I'm concerned upper area of the muffler will be just a trapped air bubble, effectively reducing the volume of water the muffler can hold before it starts sending water up to the exhaust manifold.

Water is not going to back up into the exhaust manifold because the exhaust gasses are coming out under some pressure/velocity. Any excess water is going to be blown out the exhaust. That is what it is supposed to do.

As long as the muffler is below the water injection point by ... whatever they say it should be... you shouldn't have to do a thing. Plug and play.

[Tim]

Attempting to fix things that don't need fixing is a dangerous path upon which to travel.

[feetup]

Don't forget that the inlet and outlet hoses also form an integral part of the muffler. Essentially, the water capacity would include everything from the exhaust riser to the inverted "U" in the outlet side.
I am also wondering why you have so little trust in the design and manufacture of an obviously successful product.

Tim J

[jollyboat]

I thought that exhaust gases are easier to compress than water and was under the impression that the introduction of new exhaust gasses and cooling water into the can that the volume of gasses is helpful in building a head of pressure to push the water out of the can - or so it would seem - I could be way off base here but it stands to reason.

[John, CD28]

Here we can see the hole I drilled inside the upper wall of the inlet tube, increasing the water holding capacity of this little muffler by 50%. We also see the epoxy where I filled the hole the drill made in the lower edge of the tube as I reached in to make the upper hole. The upper hole is inside the body of the muffler, and serves as a vent between the upper section of the body and the inlet tube.

A muffler must have sufficient water holding capacity so that the water that falls back down from the high loop when the engine is shut off falls into and stays in the muffler. I know the water density after the muffler is only about 50% (exhaust gas/water), but it's still important. With 30-40 inches of hose length to the top of that loop, it's easy to imagine a muffler with just 36 oz capacity being filled and sending some of that water up the inlet exhaust hose toward the manifold. I don't like the idea of using the hose between the exhaust manifold and the muffler as reserve capacity; in rough water or following seas, that could easily find its way up into the motor.

With the capacity of this tiny (6.5" x 6.5") waterlift muffler increased from 36oz to 54oz, I'm 50% happier with the muffler now. I'll go ahead and install this down low and near center where it belongs, but I think this vent hole should be there from the factory. It's easy to think the entire volume of the cylinder is the water holding capacity, but it just ain't so.

John

P.S. Yes, that's adhesive backed heat shrink tubing I used to increase the inlet tube from 1.5" to 1 5/8". It works fine, and with the adhesive inside, it's waterproof.

[Maine Sail]

I really think you are over analyzing this in big way. I have a similar sized water lift muffler on a 44HP four cylinder Westerbeke and the volume of water that will fall back down from the high loop has never even been at the top of the inlet tube when I've removed the hose. I've removed this hose about 8-10 times to work in that area.

The critical points, as previously stated, is that the water lift is located well bellow the exhaust elbow..

Re-engineering the volume of this muffler may interrupt the design flow to inlet exhaust pressure curves and could potentially cause more problems that you have not yet anticipated. It is my understanding that the exhaust gases need more chamber than the water volume in order for a water lift to operate correctly and the inlet/outlet tube insertion depths are designed to the volume of the individual mufflers volume..

My advice would be to plug the holes you drilled, fire up the motor, and do a few disconnects of the hose, after running the engine, to check your theory. Even if your theory pans out the water lift MUST still be locate LOWER than the exhaust injection elbow!

[John, CD28]

Even if your theory pans out the water lift MUST still be locate LOWER than the exhaust injection elbow!

Yes, this is mandatory. The muffler must be well below the elbow - always.

My concerns are partly based on observation of my Vetus LP muffler. The Vetus inlet tube is at the top of the muffler body, and the inlet tube doesn't go into the body of the muffler at all. I think the water holding capacity of the Vetus is nearly 100% of the volume, a full 1 gallon. The Vetus design suggests there is no need for airspace within a muffler that isn't running. Of course the exhaust tubes on both terminate near the bottom, where they need to be to form airspace as the motor runs.

I'm hoping you're right, and this little muffler was adequate from the start. However, I do feel it's better now, with the ability to hold 50% more water. I see no way the vent hole can cause trouble.

I'm going to install the little Naqualift this afternoon, as the 7" square base fits down low where the 14" long Vetus LP doesn't on my boat. Then, I set off for 2 weeks of southward sailing (Block Island, Cuttyhunk, Tashmoo?).

I appreciate all the thoughts and input. Wish me luck!

Best,
John

[John, CD28]

Bad weather killed my cruising plans, but I'm still claiming victory on this one. The little Naqualift (significantly smaller than a Vernalift) works like a champ. I've got 12 hours on the new motor (Betamarine) and all is well. The motor fires right up, the muffler muffles, the exhaust exhausts, and the PSS shaft seal is yet to let in a single drop.

Maybe over next winter I'll put some small triangle supports under the new muffler shelf, and trim the shelf up to the edge of the muffler to clear up access to the shaft again. Or, maybe I'll see if a top inlet style Naqualift will sit more directly (better centered) under the exhaust manifold.

I just want to thank you guys for helping me overanalyze this to victory!

Cheers,
John
P.S. Victory Deferred: Looking at this image, if the boat gets knocked down to port the muffler will unload its water toward the motor. I'm moving the muffler to the port side, and going with a top in/top out model. Yes, muffler #3! This will place the muffler directly below the exhaust manifold.