Anti syphon valves

[gnarley]

Do any of you leave the anti syphon valve in your fuel tanks? Did you remove your's? If so why?

[Blown 472]

gnarley:
Do any of you leave the anti syphon valve in your fuel tanks? Did you remove your's? If so why? Took it out as it was a major resritction. If tha damn thing catches fire, swim to shore and call tha insurance man.

[hoolign]

How do these work?

[gnarley]

Typically they are the last fitting that exits the tank from the fuel pickup. It looks on the outside like a std fitting, BUT when removed & on closer inspection when you look at the entrance side of the fittings it looks like there is a ball bearing in the ID of the fitting that seals the ID from flowing. It totally looks like it WILL restrict the fuel flow. I am removing mine & either want to upgrade the flow by installing a std nipple or see if I can get a higher flow anti syphon valve to replace the smaller one. If not I may just need to install a manual ball valve to shut down fuel supply if needed & hope to hell I never have the need.
What could really cause me to need an anti syphon valve anyway? The lines would need to be cut below the tank & how in the world would that happen?

[hoolign]

I wish i would have known about these things 2
years ago!my fuel hose sprung a leak in a corner before the fuel pump...was'nt pretty
thanx for the explanation

[gnarley]

[QUOTE]Originally posted by hoolign:
I wish i would have known about these things 2 years ago!my fuel hose sprung a leak in a corner before the fuel pump...was'nt pretty
thanx for the explanation
Did your boat cook? Do you inspect all your fuel lines every year?

[mike37]

anti syphon valve in your fuel tanks
would be to keep fuel from syphoning out of you carb or fuel system back to your tank
it would not stop fuel from syphoning out of the tank

[hoolign]

Did your boat cook? Do you inspect all your fuel lines every year? [/QB][/QUOTE]
http://www.***boat.com/image_center/data/500/433F1150013-med.jpg
I do now! :D

[gnarley]

mike37:
anti syphon valve in your fuel tanks
would be to keep fuel from syphoning out of you carb or fuel system back to your tank
it would not stop fuel from syphoning out of the tank OK great! But really what good is that going to do? If you think about it, it would ONLY work in that direction. If worked the other way you couldn't flow fuel to the engine! So why would you worry about fuel returning back to the tank?

[HalletDave]

Originally posted by mike37:
anti syphon valve in your fuel tanks
would be to keep fuel from syphoning out of you carb or fuel system back to your tank
it would not stop fuel from syphoning out of the tank Wouldn't the pressure from having fuel in the tank prevent this from happening (connection @ the bootom portion of the tank)? How does it siphon past the fuel pump providing the diaphragm is in good condition? Isn't that why we set up our carbs to proper float levels? Am I missing something here, or just out in the cat tails? Not trying to stir it up or piss anyone off. :D
HD

[mike37]

HalletDave:
Originally posted by mike37:
anti syphon valve in your fuel tanks
would be to keep fuel from syphoning out of you carb or fuel system back to your tank
it would not stop fuel from syphoning out of the tank Wouldn't the pressure from having fuel in the tank prevent this from happening (connection @ the bootom portion of the tank)? How does it siphon past the fuel pump providing the diaphragm is in good condition? Isn't that why we set up our carbs to proper float levels? Am I missing something here, or just out in the cat tails? Not trying to stir it up or piss anyone off. :D
HD Just my .02 but it wont work the other way you couldent pump fuel out
I dont think you need one
but mybe it woud prevent fuel from being suked out of you carb whin fuel tank temp goes down craets a vacume

[HalletDave]

but mybe it woud prevent fuel from being suked out of you carb whin fuel tank temp goes down craets a vacume
I thank this would only occur if the tank was empty, carb sitting higher than the bottom fuel line connection to the tank. I still think the pressure from having fuel in your tank will prevent this from happening. Fuel tanks are vented to prevent vacuum from occuring. I guess I will find out if it ever happens to me. wink
HD

[hoolign]

There should'nt be a vaccum on fuel tanks
there vented!

[mike37]

Lets go over to gnarley house take his tanks out so we can see wats up
my tank draws from the top

[hoolign]

your tanks cant draw from the top,other wise youd run out of fuel as soon the level dropped beyond the pick up

[mike37]

there is a drop toob that goes to the bottum of the tank

[gnarley]

Yeah on the top of my tank is the large inlet pipe, then there is a smaller vent fitting with a hose that runs to the vent fitting mounted to the outside of the hull then there is the feed fitting that has a drop tube that goes to the bottom of the tank.
I can't pull it out yet to check the tube for an internal tank filter, as the tank is full & the bow is sitting higher right now than the transom so all the fuel is at the rear of the tank where the fittings are. As soon as I can I will pull out the syphon tube & inspect it for a filter, debris or diameter to ensure free flow of fuel! I had a hell of a time last year & want to make sure EVERY item is inspected in my fuel system!

[hoolign]

Right,so it draws off the bottom, dave the only actual vaccum that is going to be created is when you run your engine for a bit to lower the level of fuel,reducing the hydrostic pressure in your tank,without suction from the fuel pump,the gas will fall back down the fuel line to the point of it being balanced with the amount of fluid in the tank

[LVjetboy]

An interesting question...wonder where it came from? :)
Fuel is always drawn from the bottom, no matter where the supply tube actually "exits" the tank. I think everyone knows this.
Siphoning can happen no matter where the supply tube actually "exits" the tank, top or bottom, as long as the outlet (or fuel line break in Holligans case) is below the tank level and there's continuous fluid in the line...hence "siphoning" I think most know this.
An anti-siphoning valves can stop siphoning even though the check valve ball is springed against the flow direction if the spring pressure on the ball is sufficient to counteract the pressure created by the difference in tank level and exit (or fuel line break in Holligans case.) I'm sure a few know this.
According to what I consider a reliable source, anti-siphon valves are installed to prevent the problem Holligan illustrated with a picture. Maybe a safety regulation for all tanks? Not sure of the exact regulation or wording.
A side benefit is they prevent siphoning from one tank to the other if you have side tanks. This benefit however, seems not mentioned anywhere (that I can find) and maybe not even mentioned in marine saftey regulations. Possibly because they were written for single tank vessels? Anyway...
I removed my anti-siphon valves because of fuel restriction* concerns. If I spring a leak in the line from the tank to the fuel pump inlet, no anti-siphon valve causes a safety hazard. If the leak is on the fuel pump exit side (pressurized) anti-siphon or no, she's gonna blow.
Using high-quality lines, AN fittings and braided steel seems a safe thing to do. That and regular maintenance. Lacking that, with cheaper rubber hoses and clamp-ons, an anti-siphon valve may be a good back-up.
In the end it all comes down to risk reduction. Nothing is guaranteed. How safe to you want to be?
*note: I've run a 400+ hp engine with dual tanks and anti-siphon valves with no fuel delivery problems. So my guess somewhere in excess of that hp before problems with fuel starvation and anti-siphon valves.
jer

[eliminator777]

I have no anti syphon valves in my tanks then again My tanks have a 1 inch bung welded in the lowest rear corner with a number 8 aero-quip line on each side of boat going to fuel filter water seprator 2 lines in 1#10 line to pump. with vents 1 on each side with #6 line. :D :D :D :p :p

[Charger455]

I had a fairly knowledgable mechanic type friend explain the possible reason for the spring loaded valve. It does stop the fuel from syphoning out. The vacuum pulled by a mechanical fuel pump will overcome the spring pressure. Additionally, since most jet boats use a mechanical fuel pump stock, (xcept newer EFI) after a every run, your fuel would flow back to your tanks. On hot days it wouldn't take long for the fuel in the carb bowls to vaporize. So on start up, you would have to crank the engine (turning the jet pump with water)long enough to prime fuel to the carb. If you have an electric pump and your drawing thru the spring pressure, it would restrict flow.

[LVjetboy]

Charger455. I agree with your mechanical friend, the spring pressure is designed to stop siphoning, yet still flow to the pump. But regardless of the fuel pump design, that spring and ball represent a restriction to fuel flow.
Now I'm not suggesting anyone take theirs out. And I don't know for a fact that there's a certain power level above which an anti-siphon valve is an unacceptable restriction. Some of that would depend on valve design, line sizes and fuel pump I'm sure. There may be some high flow check valve out there...a little more expensive...but the hot ticket.
But I'm just curious about this topic because these little suckers don't get talked about much.
jer

[gnarley]

I'm glad I started something here. What's the trade off, safety verses supply needs for increased HP? Some tanks just don't provide adequate delivery means when you are reaching for additional HP & you need to supply more fuel to it. So there comes the paradox, more HP without the safety of an anti siphon valve or the safety of having it & not flowing enough fuel to make the HP. There has to be a better way or a way to prevent siphoning without the reduction in fuel flow. Are there any in-line anti siphon valves that don't attach directly to the tank?

[LVjetboy]

Gnarley, I was wondering that too. All it is is a check valve. I'm assuming most racers and those with big hp engines run without anti-siphon valves? I would like to know this.
I did a quick search online when this subject came up on the other board and found several different check valves with flow and pressure drop specs. I even found some anodized aluminum ones. Most likely there is a low restriction check valve suitable for big hp...with enough spring pressure to shut the tank off in case of a leak.
So it may not be an either or thing after all. Just needs someone to find the right combo.
jer

[gnarley]

LVjetboy, can you post the link to that other thread you mentioned? I will call & find out if I can determine the mfg.
Thanks

[LVjetboy]

Sure, no problem. There's actually two threads, the first one started by CaveFish:
http://www.banderlog.com/dcforum/DCForumID1/2641.html
The second by Apollo:
http://www.banderlog.com/dcforum/DCForumID1/2810.html
Maybe not the most exciting reading, but some interesting comments by OldRigger and others.
jer