anti-siphon valves

[bob johnson]

I had asked a few questions about my future fuel tanmks up in the front of my boat.
One suggestion was to make sure I have anit-siphon valves on my fuel tanks.

I see mention of them in several posts...so they seem to be something that should be used.

I went shopping online for my stuff and found some anti-siphon valves but they have barbed ends for use with hoses.

and they have a pipe fitting on the end that goes into the tank..

my problem with that is i want to have a dissconnect at the tanks and was going to use johnson quick dissconnect fittings....that themselves go onto the 3/8th" ID hose.

if I put the anti-siphon valev into the 1/4 npt female opening in my new portable tanks...Ill have to attach a hose to the end..

do they make an anti-siphon valve with a female 1/4 npt opening...so I can them plug my male omc quick dissconnect fitting into ?

I want to be able to pull the tnaks from their storage bays for refueling..and mixing my oil.....

so what ever I use I need to still have the quick dissconnects in the system

thanks

bob

 

[emdsapmgr]

Re: anti-siphon valves

Don't know if you need them. Anti-siphon valves keep the fuel from draining back into the tank once the engine is shut off. This is more of a problem with carbed engines that have carb vents. Usually, you can run all day with constant starting and shut offs without problem. After a day or two, the fuel may begin to drain back into the tank. My normal starting procedure is to pump up the primer bulb before starting the engine each boating day. This bulb priming negates the need for an anti-siphon valve. In rare instances, the ball valves in the anti-siphon valve can accumulate dirt or debris which will prevent them from flowing fuel properly. I pulled my anti-siphon valve out for this very reason.

 

[bob johnson]

Re: anti-siphon valves

the description of the valves says they are CG approved per some spec!!!

that makes it seem like an important part of the system.

for all i knew i would have guessed there might have been some anti-siphon feature in the pick up tub inside the gas tank!!

still i have a decision to make wether i can get them installed and still use quick dissconnects

bob

 

[Fl_Richard]

Re: anti-siphon valves

The fuel bulb has an anti-syphon valve built into it, if you have a bulb, you have an antisyphon valve; thats why the fuel only goes one way.

 

[Silvertip]

Re: anti-siphon valves

The purpose of an anti-siphon valve is NOT to prevent fuel flowing back to the tank from the engine. It is to prevent fuel from flowing from the tank under siphon action into the engine in the event the float/inlet needle and seat or any other malfunction in the fuel system occurs. This can't happen if the fuel tank is lower than the engine but it can easily happen if the tank is higher than engine as is the case with portable tanks. Filling the engine with fuel can make a very big "bang" and lots of fire. Primer bulbs have an inlet and outlet valve. Without them they would not pump. These are not anti siphon valves. They do allow a dribble fuel if you let the hose hang hover the end of the boat.

If you are using a fuel selector valve, install an anti-siphon valve at the output of the valve. This will not protect the system between the tanks and the valve but it would allow you to use the standard quick disconnects.

 

[MikDee]

Re: anti-siphon valves

The antisiphon valve has more then one purpose, the main purpose it is to keep fuel from siphoning out of the tank, in case of a boat accident, or fire.

 

[bob johnson]

Re: anti-siphon valves

........ It is to prevent fuel from flowing from the tank under siphon action into the engine in the event the float/inlet needle and seat or any other malfunction in the fuel system occurs. ..............
.

this is slightly confusing..trying to figure the difference between fuel supply one way and some type of siphoning in the same direction??

what is the difference...how can a device prevent fuel flow one way when the motor is off and allow it to flow when it is on in the same direction??

anyway

I could easily add the anti siphon fittings on the three way fuel selector.

now do i want to have a short section of hose then a solid pipe fuel line to my three way selector, and then solid to my fuel seperator

or do I just want to have one less connection and run gas line hose from the tank to the three way selector???

someone suggested a solid fuel line running under the floor. I could do that..it juts makes for another connection...because i want the quick dissconnect at my portable tanks

thanks guys

bob

 

[ezeke]

Re: anti-siphon valves

The coast guard required anti-siphon valve has nothing to do with flow into the tank, but is as silvertip described.

In operation, when any part of the fuel line or the engine is below the level of the fuel tank, they are still required on built-in tanks.

See: http://www.uscgboating.org/safety/boatbuilder/fuel/183-568.htm

 

[CaptOchs]

Re: anti-siphon valves

Don't know if you need them. Anti-siphon valves keep the fuel from draining back into the tank once the engine is shut off. This is more of a problem with carbed engines that have carb vents. Usually, you can run all day with constant starting and shut offs without problem. After a day or two, the fuel may begin to drain back into the tank. My normal starting procedure is to pump up the primer bulb before starting the engine each boating day. This bulb priming negates the need for an anti-siphon valve. In rare instances, the ball valves in the anti-siphon valve can accumulate dirt or debris which will prevent them from flowing fuel properly. I pulled my anti-siphon valve out for this very reason.

Silly question, but are the anti-siphon valves built into the tank? I have a Tempo 16.5 gallon (see:http://www.foreandaftmarine.com/2-640030.htm ) and my primer bulb keeps collapsing. I've changed fuel lines, but it didn't help. I tried to pry the fuel line fitting off the tank but it was difficult and I gave up because I didn't want to break the tank. I was going to try bypassing the fuel filter/water separator first to see if its a clogged filter.

 

[Chris1956]

Re: anti-siphon valves

Antisiphon valves are normally standard on permanent fuel tanks. I have never seen one on a portable tank. They do clog and restrict fuel flow to the motor.