Hunter 34 - Exhaust elbow siphon break

[paultech]

Hello,

My 1986 Hunter 34 Yanmar 3GM30F has a siphon break between the exhaust elbow (that's being replaced), while looking at other hunter 34 i've not seen a break installed.
I suspect a P.O upgrade but interested in the groups take

thank you

 

[kloudie1]

The break was installed by Hunter on my '84 model H-34. Picture attached; you can see it on the back wall. The little check valve on top failed many years ago .. I found an exact replacement and its been fine ever since.

 

[dlochner]

The siphon break must be above the waterline and be vertical. It does nothing when lying on its side.

If the engine is above the waterline, then a siphon break isn't necessary. If it is below the waterline it needs a siphon break to prevent water from back filling and flooding the exhaust manifold and cylinders.

 

[paultech]

The break was installed by Hunter on my '84 model H-34. Picture attached; you can see it on the back wall. The little check valve on top failed many years ago .. I found an exact replacement and its been fine ever since.
View attachment 236265

Thank you for confirmation! That makes sense. Curious why the mix of straight connection vs siphon break. Wonder if a certain year started that?

The siphon break must be above the waterline and be vertical. It does nothing when lying on its side.

If the engine is above the waterline, then a siphon break isn't necessary. If it is below the waterline it needs a siphon break to prevent water from back filling and flooding the exhaust manifold and cylinders.

Agree its current configuration is not ideal, part of what prompted this post was to find how other Hunters are setup. Plan to correctly mount the break.

Oddly I believe the exhaust elbow is above the waterline but Hunter clearly installed these factory for a reason so I may be incorrect

Fred of epitomes fame seemed to have removed his given its above water line.
I think the big benefit it provides for overcranking? If overcrank without starting (no exhaust pressure) with seacock open then could flood the muffler and upto the exhaust elbow

 

[Allan12210]

Mine (1985) was exactly the same as Kloudie's. Are there any witness marks on that sound proofing material (compressing or old screw holes)?

 

[paultech]

Mine (1985) was exactly the same as Kloudie's. Are there any witness marks on that sound proofing material (compressing or old screw holes)?

Need to validate in person but I do believe so. Very similar to where Kloudie has his mounted.

 

[Ralph Johnstone]

I had the little vacuum breaker leak once and it was a
%$#^&%*(^$)&* mess.

I measured the water level using a clear vinul tube attached to the engine raw water thru hull. The bottom of the mixing elbow was about 4" above the water line. Close enough for me just to avoid another mess and paint job like that again and over the side went Hunter's vacuum breaker assembly. After chucking the mess, I tested the raw water throughput (with the engine off) with about 24" of head on the engine cooling system and found no raw water leakage due to the sealing of the raw water pump :

​

The 4" measurement is to the bottom of the of the mixing elbow inversion just in case the dam should ever corrode through as this one is getting close to.

​

 

[jssailem]

Agree its correct configuration is not ideal,

The design of a siphon break is not determined by the boat or its builder. It is an independent tool used to prevent the backflow of water when the engine stops. It must be oriented so that he hoses are vertical and the siphon break part is above the two hoses. This is physics, not builder or owner optional.

For your own safety and that of your boat, please repair it. From looking at your image, the Previous Owner did not understand the function. Perhaps the attached hoses were too short. I would get longer hoses so that the siphon break can be oriented like the unit, as shown in @kloudie1's image.

 

[paultech]

The design of a siphon break is not determined by the boat or its builder. It is an independent tool used to prevent the backflow of water when the engine stops. It must be oriented so that he hoses are vertical and the siphon break part is above the two hoses. This is physics, not builder or owner optional.
View attachment 236269

For your own safety and that of your boat, please repair it. From looking at your image, the Previous Owner did not understand the function. Perhaps the attached hoses were too short. I would get longer hoses so that the siphon break can be oriented like the unit, as shown in @kloudie1's image.

( I had a typo where I meant to say "the correct current configuration is not ideal ")

I do understand its role and purpose, my question was regarding the mixed deployment by Hunter. You see Hunter 34's with and without the siphon break (as the exhaust elbow inlet is above the waterline) so was trying to collect a consensus on their deployment.

Current plan is to fix the current siphon break mounting but I am interested in the multiple reports (even by those that have done ocean crossings in their hunters) regarding the removal of the siphon break on their boats

 

[kappykaplan]

The siphon break must be above the waterline and be vertical. It does nothing when lying on its side.

 

[dlochner]

( I had a typo where I meant to say "the correct current configuration is not ideal ")

I do understand its role and purpose, my question was regarding the mixed deployment by Hunter. You see Hunter 34's with and without the siphon break (as the exhaust elbow inlet is above the waterline) so was trying to collect a consensus on their deployment.

Current plan is to fix the current siphon break mounting but I am interested in the multiple reports (even by those that have done ocean crossings in their hunters) regarding the removal of the siphon break on their boats

Installing a siphon break is fairly low cost. Not having a siphon break when one is needed can lead to a very high cost event. Seems like a simple decision to me.

The valve on the type of vent you have can become loose. A wrench quickly and easily fixes that problem.

 

[Johnb]

In a Hunter 34 if there was no anti siphon valve and water was siphoning in:

where would it be coming from?
where would it be going to?

 

[dlochner]

In a Hunter 34 if there was no anti siphon valve and water was siphoning in:

where would it be coming from?
where would it be going to?

Same with any engine, water comes into the engine cooling through hull and out into the exhaust system and engine block.

 

[Johnb]

Same with any engine, water comes into the engine cooling through hull and out into the exhaust system and engine block.

How does it siphon though the raw water pump? Note the question was specifically when siphoning.

 

[kloudie1]

Consider when the engine is shut down after running. The raw water hose will be full and if there is any seepage past the pump impeller, the water would siphon into the muffler and flood the engine. The siphon break stops that..

 

[dlochner]

A siphon is a low probability event with a low cost prevention method to avoid a disastrous consequence.

 

[Davidasailor26]

I think the big benefit it provides for overcranking? If overcrank without starting (no exhaust pressure) with seacock open then could flood the muffler and upto the exhaust elbow

The anti-siphon won’t do anything to prevent that though. When overcranking the water is being actively pushed into the exhaust, and will back up to the lowest point, which is usually the cylinders. That’s different from passively siphoning water up from a source.

 

[Terry Cox]

My 1986 Hunter 34 Yanmar 3GM30F has a siphon break between the exhaust elbow (that's being replaced), while looking at other hunter 34 i've not seen a break installed

Wrote a somewhat related article a few years ago about the vacuum break on our boat. Different model, but ... The link to that article below.

Main Engine Vented Loop

Well, what an experience. Took the fam out around the islands for a two week cruise during the July 4 celebration. Noticed a more than normal amount of sea water in the main bilge after each shut down. Also, quite a bit of seawater in the bilge beneath the engine that was never there before...

forums.sailboatowners.com

 

[Johnb]

Consider when the engine is shut down after running. The raw water hose will be full and if there is any seepage past the pump impeller, the water would siphon into the muffler and flood the engine. The siphon break stops that..

Thanks