Engine raw water siphon break

[Skipper]

I'm troubleshooting a reduced raw water flow issue - other thread.
Started wondering again about the siphon break. Just a curiosity.
-see pic-
It's just a T fitting, with the hose on the left coming from the HX, and the one on the right (blue stripe) going to the elbow. The 3rd hose runs aft along the underside of the cockpit sole, then down to attach at the exhaust outlet on the inside of the transom.
If there is any back pressure at all from the elbow, i.e. A partial clog, wouldn't the raw water naturally take the easy path and just dump through the siphon break, thereby bypassing the entire exhaust system?
I mean, this is great for keeping the water flowing through the HX if the elbow completely clogs, but then you've got a hot elbow, and no way to know because water is still flowing out the back.
And couldn't this reduce flow to the elbow anyway even without a clog....
Should it be a different setup, valve etc instead?

 

[capta]

I'm not sure what that is a picture of, but it does not resemble any anti-siphon valve I've ever seen. If it has been working, then I'm guessing you don't need one.

 

[Skipper]

I'm not sure what that is a picture of, but it does not resemble any anti-siphon valve I've ever seen. If it has been working, then I'm guessing you don't need one.
View attachment 143628

It's a T fitting.
I share your suspicion, no valve.
So if I don't need a siphon break, why is the T installed, and the hose running to the exhaust outlet at the transom?

I think it's Bristol's version of a siphon break. And/or an elbow bypass should it clog. I'm still wondering about the other questions IE cooling water intended for the elbow actually escaping out the siphon break, or how to know if elbow is clogged when water is still running out the back.
I don't think it's an issue or relevant to my troubleshooting the suddenly reduced raw water flow. Just a curiosity. I've never had flow problems before so the setup works.

 

[Gunni]

First step in resolving a reduced cooling water flow would be to get your antisiphone loop right. That rig you have looks to be sending cooling water down to your transom where it does no good cooling your elbow or muffler.

 

[FastOlson]

Looks like the standard factory fitting on my 3 cylinder Universal diesel. Mine exits the transom via a 1/4" hose that goes downhill from a high point in the engine compartment.
Some builders put this exit into the inside of the metal exhaust fitting at the transom. Ours uses a separate little thru hull fitting just above the exhaust.

 

[heritage]

I had a 1976 Westerly that has a similar T-fitting instead of the typical anti siphon valve. The line that acted as an anti siphon was very small and emptied into the cockpit under the teak floor boards. While the engine was running, I would always see a small but steady stream of water running under the boards and down the cockpit scupper. An archaic system maybe, but simple and never had a problem with it.

 

[Gunni]

The antisiphone is designed to keep a flooded exhaust system from back flowing into the exhaust valves and engine. If your exhaust elbow is clogged and not producing enough gas pressure to evacuate the exhaust system you have the potential to fill the system with raw water where it represents a threat to your engine, especially when off.

What you have looks to be a parasitic raw water discharge that loses water regardless of conditions at the exhaust elbow. Sort of like a small outboard where raw water sprays out of multiple ports because the system produces far more raw water than needed. And the engine cylinders are protected.

 

[Skipper]

What you have looks to be a parasitic raw water discharge that loses water regardless of conditions at the exhaust elbow. Sort of like a small outboard where raw water sprays out of multiple ports because the system produces far more raw water than needed. And the engine cylinders are protected.

Interesting.
That would make sense, given the operational success of the system.
Except when the HX inlet clogs...
And so simple to figure out: more water than needed. Sometimes we make things more complicated than they are