Active bypass siphon valve

[Rowan]

Hi all, first time poster.

After reviewing the great resources on this site about exhaust systems and how they apply to my yacht, one of the pieces of information I have failed to understand is what exactly the anti-siphon bypass is as mentioned below and found on this page https://www.sbmar.com/articles/designing-a-marine-exhaust-system/

Quote:

“The general layout of the “anti-siphon” valve. In reality, it’s not a valve at all, but an active bypass that should be installed on the uphill water flow before it goes over the top, and discharged over the side above the waterline in a VISIBLE location. This allows cranking without flooding the lift muffler and adds an enormous layer of safety to the system.”

I am confused by what exactly this Active Bypass is?  In the pictures it looks like it’s just a Tee?

If that’s the case, what stops the raw water just running out that and not going into the exhaust mixer?

Thanks

Topic

[Clark Leighs]

A photo or two might help elicit better help.     

An active bypass as you referred to it is literally a bypass where it has been determined that there is too much raw water exiting through the exhaust system,   TO much water can cause higher back pressure than the engine can tolerate  for proper performance.    

This bypass can only be done when it has been determined that adequate cooling water still flows through the exhaust system to keep it cool. 

Usually there is a valve at the tee so the bypass flow can be adjusted to ensure adequate flow of the main exhaust allowing ONLY the excess to bypass.

 

A lot of people refer to this as a spitter which can serve another purpose,  tell the operator that there is indeed raw water flow.   The primary purpose though is as described above.

 

 

[Author]

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