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Old 12-05-2010, 18:29   #1
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Custom Exhaust Elbow Design

I'm changing out the exhaust elbows on Volvo MD2030B's to a different design made from stainless instead of cast iron. The pic below shows the basics of the design change. Instead of an outer water jacket around the exhaust (green one), the exhaust comes out hot, and water is injected further downstream via a rubber hose to a hose barb (the stainless one in pic). My question: should that hose barb be a consistent diameter and be welded to outside of large pipe? OR... Should the inside end of the hose barb be some type of spray nozzle and extend inside the pipe? I found a welder to make this, but he isn't marine exhaust specialist. If there is some serious engineering involved in a spray nozzle, I will have to find a specialist. Thanks for the help.
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Old 12-05-2010, 18:33   #2
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I don't think you need a spray nozzle. I'm not sure how well stainless steel will stand up to hot sea water mixed with exhaust, however.
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Old 12-05-2010, 18:39   #3
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I don't mind this stainless elbow IF the hose barb goes into the main tube and bends 90 degrees to the outlet.
Terminating the barb at the tube wall and spraying water will cause some backwash up stream.
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Old 12-05-2010, 18:47   #4
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You can see some pictures of custom elbows here

Marine Exhaust Risers And Elbows 316L Stainless Steel Inconel 625
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Old 12-05-2010, 19:01   #5
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You should and see what Stainless Marine in Fl has to offer
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Old 12-05-2010, 19:07   #6
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Nice work. Nice price.

Diesel Risers and Elbows
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Old 12-05-2010, 19:26   #7
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You might want to check out this thread before making a final decision: DIY exhaust elbow - which metal? - Yachting and Boating World Forums
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Old 12-05-2010, 19:40   #8
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Here is a link to a picture of a not very old stainless exhaust elbow. Both engines needed them replaced.

(Blog) [KensOtherBlog] The Last Entry: Greetings all!...
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Old 12-05-2010, 20:03   #9
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Deep Freeze & Ziggy: Thanks for all the great inputs. The polished custom elbows on the suggested web sites look great, but the prices are steep. I refuse to put new OEM cast iron elbows on because they rust, crack and can't be cleaned out. Although, stainless has it's own problems according to the other discussion board.

Never Monday: Thanks for your input. I showed a simplified version of the planned design because the pic clearly showed the hose barb. That elbow version is also standard on the engines, but I have the more complicated (and pricey) riser version. The pics below shows more specifically the configuration I want, but it doesn't show the injection hose barb. Assuming the injection hose barb is angled 45 degrees downward into the pipe, do you think that would work well with just a straight hose barb?

The other advantage of this design is that the seawater shouldn't contact any of the welds which sounds like an issue with stainless.
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Old 12-05-2010, 21:10   #10
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The exhaust on my perkins 4-236 is made of screwed together 1 1/2 inch black iron pipe similar in configuration as your pics above. I replace it every 3-5 years. Inexpensive and easily replaceable. All of it wrapped with any kind of high temp insulating wrap.
The last section is 316 pipe with a 1/2 inch piece 316 tubing welded to it as the water injector. It is still in good shape after 10 years of use. As long as the water gets into the exhaust it does the job of cooling it.
No hose barbs of any kind, just double hose clamps.
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Old 13-05-2010, 04:43   #11
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Greg,
This pic shows good placement of the water inlet. It looks to be about an inch below the seam of the second 90deg bend. Go for it!

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Old 22-05-2010, 16:52   #12
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Quote:
Originally Posted by never monday View Post
Greg,
This pic shows good placement of the water inlet. It looks to be about an inch below the seam of the second 90deg bend. Go for it!

Thanks Never Monday,

I modified this design a little bit and sent a PVC mock-up to have it made out of stainless. I should get them back next week and estimated cost was $175/ ea.
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Old 23-05-2010, 03:58   #13
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Thanks Never Monday,

I modified this design a little bit and sent a PVC mock-up to have it made out of stainless. I should get them back next week and estimated cost was $175/ ea.
looks good, got anymore pics?
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Old 23-05-2010, 08:02   #14
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I have a pair of stainless steel exhaust risers on a couple Cummins B-series turbo diesels that get a lot of use. These risers outlasted the first engines and are now bolted on to their second set of engines. These risers do have an internal nozzle with ports that spray back towards the exhaust hose.

To me it seems like a false economy to have cast iron risers if they need to be changed out more than once during the life of the engine.
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Old 23-05-2010, 11:01   #15
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looks good, got anymore pics?
Attached are a few more pics of my PVC model. I should get the stainless elbows back this week and will post some pics of finished product.

Thanks to all for the help.
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