The Dreaded Anti Siphon Valve

[Merc4ever]

Like so many boaters I was stranded without fuel getting to my engine and removed the anti siphon valve from the tank. I know the Coast Gaurd wants you to keep them so the fuel doesn't drain into the bilge in case of a leak but I left it out like everybody does, so I keep running smoothly.

My question is my engine compartment always has a strong fuel odor but there's no wet spots. Does not having the anti siphon valve make my carb leak fuel ?

 

[artificialreef]

Re: The Dreaded Anti Siphon Valve

Are you joking?

 

[Merc4ever]

Re: The Dreaded Anti Siphon Valve

No joke, 3 of us I know have removed it because it stuck and we were stalling out. Now we all run smooth. Was this stupid? Is it why I have the odor?

 

[90stingray]

If you know its wrong, then why not purchase the correct replacement part? Yes its stupid to knowingly run without one. And no, would not cause odor. You have a leak...

Sent from my DROIDX using Tapatalk

 

[fmalott]

Re: The Dreaded Anti Siphon Valve

Are you joking?

doesn't sound like joking to me. anyways the valve stops the gas from going back into tank if you have no valve it's going back into tank as far as your fuel smell it has nothing to do with your valve. when the carb bowl fills up the needle should close the fuel flow if the fuel is going back into the tank because of no siphon valve then of coarse there is no fuel in the bowl to keep the needle closed so maybe your getting fumes coming from the carb. my valve failed last year all i did was put a shutoff valve on and i use a primer ball to fill the carb bowl the primer ball keeps the fuel in the carb and it stops it from going back to tank and my boat runs great. i would take a closer look at your carb to see if your needle and seat are working properly

 

[Lyle29464]

Re: The Dreaded Anti Siphon Valve

Great thread. Just learned how to make a bomb.

 

[Pete104]

Re: The Dreaded Anti Siphon Valve

Dumb & Dumber pt 2.

 

[stonyloam]

Re: The Dreaded Anti Siphon Valve

the valve stops the gas from going back into tank

It does that, but that is NOT its primary function. The primary function of the anti siphon valve is to keep gas from coming OUT of the tank should the fuel line develop a leak in the portion of the fuel line that may be below the level of the gas in the tank. If the line were to develop such a leak the fuel would continue to drain (siphon) into the bilge until the level has dropped to the level of the leak hence the anti-siphon part of the name. If you can smell gas in the bilge then you have a potentially deadly situation on your hands, you need to find out where it is coming from. I also believe that a primer bulb in the line is also unwise and illegal.

 

[Pete104]

Re: The Dreaded Anti Siphon Valve

I probably should have been as polite as Stoney.

If you can smell gas, there is leak!

 

[Merc4ever]

Re: The Dreaded Anti Siphon Valve

I probably should have been as polite as Stoney.

If you can smell gas, there is leak!

No problem, stupidity deserves a good slam. I admit I was dumb about the purpose of the anti siphon valve, thanks for the info.

 

[sschefer]

Re: The Dreaded Anti Siphon Valve

If you have a newer poly gas tank they do have a certain allowable amount of permutation that will cause a fuel odor in the bilge area. The anti-siphon valve is mandatory by USCG regs and although I sympathize with your reason for removing it I would replace it for insurance purposes if nothing else. The fact that you removed it is proabably not your odor source unless you replaced it with a valve that isn't rated for fuel and it's leaking. It only takes a couple of drops to vaporize into a pretty heavy odor and explosive mixture in an enclosed area.

I have a 35gal poly tank and can smell fuel odors in my bilge so I installed a bilge blower just as a precaution. I've acutally had people ask my why I have a bilge blower when I have an outboard. I just tell them I like being safe.

 

[fmalott]

Re: The Dreaded Anti Siphon Valve

It does that, but that is NOT its primary function. The primary function of the anti siphon valve is to keep gas from coming OUT of the tank should the fuel line develop a leak in the portion of the fuel line that may be below the level of the gas in the tank. If the line were to develop such a leak the fuel would continue to drain (siphon) into the bilge until the level has dropped to the level of the leak hence the anti-siphon part of the name. If you can smell gas in the bilge then you have a potentially deadly situation on your hands, you need to find out where it is coming from. I also believe that a primer bulb in the line is also unwise and illegal.

just think about it first before the rude comments get said, the valve only stops the fuel from comimg out when the motor is off when the motor is running the valve is open so regardless if i have a valve or a shutoff valve gas is being drawn in the line if there is a leak in the line with the motor running fuel will leak out with a shutoff or anti siphon valve, so with that being said when i shut my motor off i also shut the shutoff valve off so if there is a leak in my line with the motor off then the shutoff will stop the fuel from leaking from my tank to the bilge.
P.S. Lyle29464 a bomb give me a break, Pete104 nice comment

 

[Lyle29464]

Re: The Dreaded Anti Siphon Valve

The valve does several things. If you do have a fire in the engine or gas tank area it can burn to the water line, burn the gas hose and most of the time the tank will not go bang. The coat guard thinks the valve should be there because they are 20 feet away trying to put the fire out.

 

[Silvertip]

Re: The Dreaded Anti Siphon Valve

To carry this one step further - fuel cannot drain out of the carb back to the tank. Look carefully at the carburetor. Notice that the fuel enters the carb float bowl at the TOP of the carb. Fuel cannot therefore, be drained from it through the top. To prove this point, fill a cup with water. Does it run out? Of course not. The ONLY time a fuel system would be safe without an anti-siphon valve would be when no part of the fuel line is NEVER below the outlet of the fuel tank. That is almost never the case. Although an outboard sits high on the transom, the fuel line and primer bulb are generally lower than the tank outlet when using portable tanks. A leaky fuel line therefore dumps fuel in the boat. An I/O generally has the engine mounted fuel pump and/or the fuel line lower than the tank outlet at some point so it too requires the valve. Outboard powered boat with built-in tanks generally have a flex line running to a bulkhead fitting where the line then runs to the engine. The tank to bulkhead fitting often has the flex line running at some point below the tank outlet. The only time fuel will not siphon is when the level of fuel in the tank reaches the lowest level of fuel line. Remember, fuel tanks suck fuel from the bottom of the tank via a dip tube. The fuel leaves the tank at the top.

 

[fmalott]

Re: The Dreaded Anti Siphon Valve

true what your saying but the line has to be lower than the tank Silvertip you said "The ONLY time a fuel system would be safe without an anti-siphon valve would be when no part of the fuel line is NEVER below the outlet of the fuel tank. that is almost never the case. your wrong in my case i have a 1983 thundercraft and the fuel tank is in the front of the boat so the fuel line goes up from the tank runs down the side of boat to the back of boat then it's runs down to the fuel pump so with no anti-siphon valve if i had a leak in the fuel line the fuel will not leak out because the fuel line is above the fuel tank

 

[stonyloam]

Re: The Dreaded Anti Siphon Valve

Whether or not a anti-siphon valve is needed is beside the point, the fact remains that it is required.

 

[fmalott]

Re: The Dreaded Anti Siphon Valve

i hear what your saying stonyloam it's almost like those guys that rebuild those honda civics for street racing there ok till you get caught so i guess if i get pulled over by the police or coast guard or who ever polices it and they see no anti-siphon valve then it's not ok

 

[Don S]

Re: The Dreaded Anti Siphon Valve

You guys are missing the point about the AS Valve. It's required to be installed by the boat manufacturer. It's a safety item. If you take it out, you aren't going to get caught by anyone who cares if you have one or not. They are there to make the boat safer and keep fuel from siphoning out of the tank if something should cut the fuel line and it drops below the level of the carb.

If you don't care about safety and think things won't happen to you, fine, leave it out. Would be handy if you had a sign on your boat to tell those going with you that one of the safety items has been removed.

If you want to be safe, install a new one, they only run a few bucks in the bigger picture. If they keep plugging up, then you should probably clean your tank out.

From the sounds of things, you have a leak somewhere, probably an aluminum tank with corrosion all over it, and maybe a pin hole through where gas can escape, hard to say. But the AS valve has nothing to do with your smell.

 

[Outsider]

Re: The Dreaded Anti Siphon Valve

'Illegal' and 'required' are such complex words, so easily bantered about. Sometimes it helps to go to the source ...


FEDERAL LAW [when manufacturing a vessel]

183.568 - Anti-siphon protection
Each fuel line from the fuel tank to the fuel inlet connection on the carburetor must:
(a) Be above the level of the tank top; or
(b) Have an anti-siphon device or an electrically operated fuel stop valve:

(1) At the tank withdrawal fitting; or
(2) Installed so the line from the fuel tank is above the top of the tank; or
​

(c) Provided that the fuel tank top is below the level of the carburetor inlet, be metallic fuel lines meeting the construction requirements of Sec. 183.538 or "USCG Type A1" hose, with one or two manual shutoff valves installed as follows:

(1) Directly at the fuel tank connection arranged to be readily accessible for operation from outside the compartment, and
(2) If the length of fuel line from the tank outlet to the engine inlet is greater than 12 feet, a manual shutoff valve shall be installed at the fuel inlet connection to the engine.

:facepalm:

​

 

[fmalott]

Re: The Dreaded Anti Siphon Valve

thanks outsider after reading your post i'm legal because my fuel line is well above the tank and carb and i have manual shutoffs. so it seems like one of those post that have alot of opinions and it's going to go know where i live in ontario canada i'm going to see what exactly what the law is. i think i hijacked the thread long enough