That is Positively, Exactly .......................
Last weekend while working at my Yanmar 3JH2E, I noticed that my U shaped cast iron mixing elbow had a hair line crack on the side. I discided to take it off and inspect it closer. Once I removed the mixing elbow, I could see that it was almost plugged solid with crud buildup inside. I called Yanmar for a replacement to find the cost close to $550 for this item. As I am not crazy about dropping $550 on this, has anyone ever heard of making one of these? I can fabricate the cast iron pipe 45 degree elbows into a U shape and drill a hole to accomodate an inlet fitting to dump seawater into the pipe. Is that all there is to this? Any experience with this would be appreciated.
Thanks.
.................. the route I would go if my Yanmar 2GM20F weren't stored in a Nike shoe box under my companionway stairs. Due to clearnce limitations in the shoe box, it's impossible to use anything but the compact "U' mixing elbow. I seem to replace it about every three years and the last cost (this year) was $382.35
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Attached is a picture of a mixing elbow I made for a friend years ago on his mid 80's Catalina 27 with an Atomic engine. He had had the boat for a good number of years and swears that the rusted out piping that had failed was the original piping installed by Catalina. It was corroded to thinner than tissue paper. He insisted that I match the original design (more like a happening) exactly. I matched the dimensions exactly (1-1/2" pipe) but used schedule 80 pipe (also referred to as "extra strong"). This is a heavier thickness than the commonly available schedule 40. Elbows and other fittings were rated at 150 PSI malleable iron. Again, commonly available.
The short vertical piece of pipe behind the water injection hose appears to be what is called a "drip leg". It's only purpose, I can see, is to catch any splashes of water which may try to head back towards the exhaust manifold. Doubtful.
If I could fit one of these babies on to my current engine in the shoe box, I would:
- Use schedule 40 pipe before the water injection. Healthy environment for steel.
- Use schedule 80 pipe after the water injection. This provides extra metal for the extreme corrosion conditions.
- Use smaller piping from the exhaust header to the water injection point. This is taken from the rather small X-sectional diameter found in the U shaped elbow (see sectioned elbow). Clogging does not start until the gasses touch the cooler metal which are cooled by the water injection.
- Make all pipe nipples (short pieces of pipe) as short as possible to avoid excessive bending loads on the exhaust manifold. This thing can become heavy if you're not careful with your dimensions.
- Increase the piping to 2" diameter just past the water injection point to match the 2" wet exhaust hose, and again, as short as possible.
- Insulate up to the point of water injection.
The schedule 80 pipe nipples are only available from a commercial piping supplier. If you decide to go with schedule 40 pipe nipples (regular piping) it just means you have to keep a closer eye on it for corrosion. This become a question of
cleaning the cold plugged portion of the thicker piping every few years OR
replacing the cold plugged portion of light piping every few years. Comes down to personal preference really. Also, don't cut or drill any of the pipe. Use all threaded pipe fittings for security against corrosion. Ensure you do not inject the cooling water in a way that could splash back towards the exhaust manifold. There is very little pressure in the piping.
Just a final suggestion to research,either here or the web, to make sure you observe correct elevations and the use of a vacuum breaker, if required, when you put this together. You don't want sea water dribbling back into your exhaust manifold :cussing:.
