syphoning

[slipper]

I have water syphoing back out of my raw water cooling system. It seems to go all the way back to the impellar.
It has happened at differant times ie: in a lock with water rusing past,sailing either tack,motoring when rough.
Would a water scoop help ?
And yes it goes through a vetus water trap as it comes in, and this just higher than the engine.

 

[Burnham Bob]

not sure i understand what you mean. from memory, a water trap is after the exhaust and before the outlet on the transom - did you mean a raw water filter? an anti syphon valve is what is normally fitted in the water hose that takes the hot water after it has been round the engine block and feeds water into the exhaust gas/cooling water mix at the exhaust elbow. as soon as the impellor stops pumping, the anti syphon valve opens, air enters the system and there is no syphon loop.

 

[Tranona]

The schematics in the Vetus catalogue www.vetus.com will show you how to construct a system to eliminate syphoning. You need an anti syphon valve downstream of the raw water pump, either before the inlet to the heat exchanger, or more commonly if your plumbing allows it in the hose from the heat exchanger outlet to the water injection point into the exhaust.

 

[Gunfleet]

http://www.goodoldboat.com/reader_services/articles/Marine_exhaust.php will tell you more about siphoning in sailing boats than any normal person could ever want to know.

 

[LittleSister]

http://www.goodoldboat.com/reader_services/articles/Marine_exhaust.php will tell you more about siphoning in sailing boats than any normal person could ever want to know.

What a great article! It's clarified for me things I have pondered for years and have never found properly addressed in many articles and manufacturers' guides. It is refreshing to be told there are a range of opinions about certain dimensions, advice about which are the most critical, and informed and qualified suggestions about various unknowns.

p.s. I never claimed I was normal!

 

[slipper]

I think i need to clear things up.
Maybe syphon is the wrong word !
Where my raw water comes in it then goes up to a fillter bowel and down to my impalla.
When the problem ocurs there is no water in that system for the impela to pull through.
Hope thats a bit clearer

 

[alahol2]

I think Slipper is talking about cooling water running back out of the engine via the intake when the engine is not running. Maybe requiring re-priming before switching back on?
If the water only runs back out to the impeller then it may not be a problem because the impeller will still be lubricated and will soon re-fill the cooling system.

 

[Tranona]

I have water syphoing back out of my raw water cooling system. It seems to go all the way back to the impellar.
It has happened at differant times ie: in a lock with water rusing past,sailing either tack,motoring when rough.
Would a water scoop help ?
And yes it goes through a vetus water trap as it comes in, and this just higher than the engine.

If alohol2 is correct in his interpretation and your problem is water draining out of the strainer and needing to re-prime when you restart the engine, then suggest you have either air getting in via hose connections or the seal on the lid, or a worn water pump allowing air in and the water to run out.

The simple solution is to close the seacock when the engine stops, but best to find the source of the air getting in.

 

[pvb]

I think i need to clear things up.
Maybe syphon is the wrong word !
Where my raw water comes in it then goes up to a fillter bowel and down to my impalla.
When the problem ocurs there is no water in that system for the impela to pull through.
Hope thats a bit clearer

Is your strainer plumbed correctly? There's usually an in and an out. Might your pipes be reversed? Correctly fitted, there shouldn't be a problem.

 

[alahol2]

Tend to agree with Tranona that air is getting in somewhere. The setup sounds similar to most (certainly my) systems. I do have a large downward loop in the pipe between the inlet filter and the water pump which I would expect to stay filled with water even if it drained out of the filter, thus giving the pump its initial priming.
PS if it drained out of that loop I would know that air was getting in at the pump end of the system.