Vetus anti-siphon valve

[Curtis]

My wife is trying to convince me that I don't HAVE to take things apart that aren't broken just to figure out how they work.

So, in this nod to her wisdom, I'll ask the question here first.

Our raw water intake for the engine has a seacock that has two hoses coming from it. The main hose is about 1.5" id and the second one, on the side, is probably 1/4- 3/8 "id. The main hose goes to a typical strainer, then to the Seafrost, then to the engine heat exchanger intake.

The smaller hose runs to the top of a Vetus anti-siphon valve that has two other hoses attached. One, the input to the valve, comes from the heat exhanger output. The output from the anti-siphon valve goes the muffler.

How does this anti-siphon valve work? What does the small line from the seacock to the anti-siphon do?

Shouldn't I just take the damned thing apart and see for myself?



Thanks for the enlightenment,

Curtis

[JGI417]

it is to prevent water siphoning back into engine when it is not running, it closes with water pressure from the engine exhaust. opens when engine stops, no pressure. there should be a litte screw cap on the top of the siphon line, when you unscrew it be careful not to lose the litte spring and rubber plug. I check mine to make sure it is free and not stuck closed. you should also have one for the head.

[Curtis]

John,
I know what an anti-siphon valve does, what I don't know is the purpose of the smaller diameter hose from the seacock to the valve. This type of valve doesn't have the spring that is externally accessable.

Curtis

[delmarrey]

Curtis once whispered in the wind:
The main hose goes to a typical strainer, then to the Seafrost, then to the engine heat exchanger intake.

The smaller hose runs to the top of a Vetus anti-siphon valve that has two other hoses attached. One, the input to the valve, comes from the heat exhanger output. The output from the anti-siphon valve goes the muffler.

How does this anti-siphon valve work? What does the small line from the seacock to the anti-siphon do?

Normally the vent from the anti-siphon valve is plumbed to the outside of the hull to see if water is (should be) coming from the small line. But apparently someone has plumbed it back into the thruhull inlet.

There are two types of Vetus valves. Type "V" allows air to siphon back into the line after the engine is off.
Type "H" actually pumps water out the so-called vent hole while the engine is running.
I suspect that you have the type "H".
One test you can do is pull the line from the air vent and start the engine. if water is pumped out of the anti-siphon valve then you have a type"H".

The way you have discribed your system, it is raw water cooled???

[markpj23]

Curtis asked....

Shouldn't I just take the damned thing apart and see for myself?

My Navy training stressed "If it's broke - fix it! If it works - find out why!"

[Curtis]

delmarrey once whispered in the wind:

The way you have discribed your system, it is raw water cooled???

Nope, it is fresh water cooled. I re-read my initial post and realized that I was inaccurate. After the SeaFrost the water goes to the raw-water pump, then to the heat exchanger.

This is the way the factory plumbed these...the picture in the owners manual matches mine. There just isn't an explanation.

Curtis

[roverhi]

Never ever rely on a anti-siphon valve to keep sea water out of your engine. The valve WILL stick shut at the most inopportune time and cause very expensive grief.

Put in a through hull and run the output of the small diameter line overboard. It's smaller diameter than the primary water line 'cause it's only there to break the siphon. Very little air needs to through this line to accomplish.

Aloha
Peter O.

[roverhi]

Never ever rely on a anti-siphon valve to keep sea water out of your engine. The valve WILL stick shut at the most inopportune time and cause very expensive grief.

Put in a through hull and run the output of the small diameter line overboard. It's smaller diameter than the primary water line 'cause it's only there to break the siphon. Very little air needs to through this line to accomplish.

Aloha
Peter O.

[Bill Houlihan]

I just replaced a vetus that was broken. On my boat the sea water goes through the vetus and back to the heat exchanger. I had to remove the spring valve mechanism from the vetus, so that sea water flowed overboard constantly (when the engine is running). I like this because I never worry about the valve clogging and no longer working.
Also I check every time I start my engine(s) and look for the overboard water stream to let me know that the sea water system is pumping.
Good Luck
Bill
San Diego

[NoTies]

I'm not familiar with the vetus valve but my first thought when I read this post was that they had added a vent line to the sea suction valve and used the antisiphon valve as somewhere conenient to terminate it. Vent lines re often added to sea suctions to mitigate any tendency to air lock due to excessive heeling, cavitation etc. If you do run the line through a separate overboard keep a close eye on things to make sure you don't get any airlocking problems. A better place for a sea suction vent is directly from the top of the strainer.