Water-cooled exhaust (syphon-break?) query

[LittleSister]

I'm trying to rationalise the exhaust system on our project boat (currently 14 joints between engine and final outlet!). The engine's a Bukh DV10.

There is a second water inlet (i.e. in addition to the exhaust elbow) into the exhaust via a small bore pipe and T piece in the exhaust, after the water lock. The small bore pipe is shown on Bukh installation drawings as coming from the highest point of the water cooling circuit, before the exhaust elbow, and joining, above the water line, the fall in the exhaust to the hull outlet. The small bore pipe is referred to as a 'bleeder pipe' on the drawing (though note the English translations of Bukh part names can be quirky).

As far as I can see this is an anti-syphon pipe (when the engine stops the water in the cooling system can fall, drawing in air via this pipe to break the syphon path). Could there be any other explanation/role for this?

If I am correct, this second inlet into the exhaust is redundant as we also have a syphon break 'piddle tube' into the c ockpit (also coming from the highest point of the cooling circuit), and I can dispense with it.

 

[VicS]

Your diagram is too small to see any detail but.....

Common systems are for the vent on the antisyphon device to have a valve which opens to admit air to break the syphon when the engine is stopped or for there to be a piddle pipe fitted instead of the valve, discharging somewhere visible. Overboard or into a cockpit drain.

The valves can salt up and fail to open or they can fail to close properly with water dribbling from them while running. The alternative overcomes theses problems.

In your case the piddle pipe ha been routed to the muffler. Neat but you lose the benefits of having a visible tell tale.

If it were mine I would reroute the piddle tube to somewhere visible.

There should be no need for a second telltale, but you do not say or indicate whereabouts on the system that is coming from.

 

[LittleSister]

Thanks, Vic.

The forum wouldn't let me upload a full size version of the drawing, but I can email it if anyone wants it and sends me an email address by PM.

I am familiar with the normal (non-exhaust) arrangements you describe, but wasn't sure if the pipe to the 'muffler' (are you turning American?) was purely a piddle pipe or perhaps had some other role.

The cockpit piddle pipe (plastic) on this boat collects from the highest point in the cooling water circuit (same place as the small bore (metal) pipe to the 'muffler') and exits in the cockpit immediately above the cockpit drain, where it is both visible and open to the air. My plan was to remove the whole of the pipe into the muffler, and leave the cockpit piddle pipe in place, but posted on here to check I wasn't ovelooking something about the pipe into the muffler I hadn't understood.

 

[Graham_Wright]

I'm trying to rationalise the exhaust system on our project boat (currently 14 joints between engine and final outlet!). The engine's a Bukh DV10.

There is a second water inlet (i.e. in addition to the exhaust elbow) into the exhaust via a small bore pipe and T piece in the exhaust, after the water lock. The small bore pipe is shown on Bukh installation drawings as coming from the highest point of the water cooling circuit, before the exhaust elbow, and joining, above the water line, the fall in the exhaust to the hull outlet. The small bore pipe is referred to as a 'bleeder pipe' on the drawing (though note the English translations of Bukh part names can be quirky).
View attachment 41642
As far as I can see this is an anti-syphon pipe (when the engine stops the water in the cooling system can fall, drawing in air via this pipe to break the syphon path). Could there be any other explanation/role for this?

If I am correct, this second inlet into the exhaust is redundant as we also have a syphon break 'piddle tube' into the c ockpit (also coming from the highest point of the cooling circuit), and I can dispense with it.

A similar pipe on my system feeds the Deep Sea Seals gland. (In this implementation it would not serve as an anti syphon of course).