What is an anti-syphon valve?

[rickdb1boat]

Are these just used in Portable Tanks or in Permanant tanks, also? I've heard them mentioned alot, but never really knew what they did. Can someone explain, as in my Permanant Tank, there is nothing in the Pick-up that restricts flow either way. It has just the Pick-up tube, going to a 90 degree fitting and then to the Motor. Thanks,

 

[kev_alaska]

Re: What is an anti-syphon valve?

Basically rick the anti-siphon valve is any valve that restricts fluid to one way travel. In my boat, I have a deck washdown system that incorporates one into the salt water inlet. It still makes me nervous having a valve below water level and you can be sure that I check it religiously. <br /><br />Ball checks in the fuel system are another type. oPump the ball and it gets hard without any flow back into the tank. <br /><br />This particular one is a flapper type anti-siphon. There are other kinds, most of the good ones are simple with as few moving parts as possible. <br /><br />Kev_alask***

 

[rickdb1boat]

Re: What is an anti-syphon valve?

I was wondering if this is something that should be in my fuel line pick-up at the Tank? Because I do get backflow to the Tank when I squeeze the primer Ball. It will get hard one time a then I hear it pushing the full back into the tank!

 

[93evinrude]

Re: What is an anti-syphon valve?

I believe it is a requirement of the coast guard that all fuel systems have an anti syphon valve in them and I would assume that yours would be where the hose connects to the tank although I am not sure.The valves that I have seen consist of a small ball bearing with a light spring.If there is a short piece of tube included in your angle valve,it is likely there.It is also possible that someone had removed the valve at some time due to problems with it,especially if there was a previous owner.<br />I removed one in a previously owned boat by knocking it out with a screwdriver.

 

[Spidybot]

Re: What is an anti-syphon valve?

Hi Rick,<br /><br />Anti-syphon is there to prevent fluid from running 'by itself'. <br /><br />Two containers connected by a hose will level by making the fluid flow to the lowest container. This principple is utilized when you wanna drain ie. the tank on a car: You place a container lower than the car's tank (on the ground), make sure the hose is filled with gas (mouth sucktion in most cases) and once the hose is full, you rapidly move the hose end down in the lowest container. By syphon the fluid runs to the lower..<br /><br />Useful also for emptying a boat providing the receiving point can be made lower (not possible when boat is on water).<br /><br />The larger distance between the upper and lower container, that fast it runs.<br /><br />An anti-syphon valve lets air into the hose and breaks the 'connection' thus preventing it from working.<br /><br />Your bulb issue sounds like you're ready for a bulb replacement. Had the very same experience and shopped for a replacement - aftermarket and original spare. Found, that Quicksilvers bulb with double valves is by far better to build and keep pressure.

 

[rickdb1boat]

Re: What is an anti-syphon valve?

So, If I,ve got this right. The bulb should stay hard no matter how many times I pump it, weather or not I have the Anti-Syphon valve in the pick-up? I had cleaned my tank due to some water issues and had found that it would get hard, but if I kept pumping, it would push fuel back into the tank. So is it the Bulb that keeps itself hard or the anti-syphon valve? I did notice when I cleaned the tank, there was a small spring inside, laying on the bottom. Do I need to replace the pick-up assembly or will it work OK this way? I know on my porable tank, it will stay firm, no matter how many times I pump it, so I don't think it is my Bulb, which is a New OMC one. Thanks,

 

[Spidybot]

Re: What is an anti-syphon valve?

Your bulb contains one or two one-way valves. When squeezing it you push fuel towards the motor, when releasing it it sucks fuel from the tank. By repeating this, you fill your carbs. etc. and by giving it a couple of squeezes after it turns hard, you build a pressure that helps filling all the fine jets and remove trapped air.<br /><br />If the valves in your bulb are not perfect, the pressure will walk backwards to the tank when a certain (not neccesarily high) pressure developes btween the bulb and the tank.<br /><br />Once the motor starts using the fuel, the bulb softens up as the pressure in the fuel line turns into a vacuum. Apart from squeezing the bulb - which makes a pressure - the motor is fed by it's own pump which sucks the fuel from the tank and relies on a perfectly tight line.<br /><br />Vacuum is what makes the syphon work, so if your anti-syph valve lets air into the hose to prevent this, your motor sucks air instead of fuel. The risc of fuel 'walking by itself' is zero in your fuel line anyway as it is closed both ends. The valves in the bulb prevents fuel from running away from the motor.<br /><br />So, one straight & tight fuel line with a proper bulb is what it takes.

 

[rickdb1boat]

Re: What is an anti-syphon valve?

Thanks for the info UU! I was just concerned about the Anti-Syphon Part IN the fuel pick-up, at the Tank. So I don't need it, right? And the Bulb should stay Hard when I pump it, weather or not I have the Anti-Syphon Valve AT the Tank? My last Question on this, Promise!!!

 

[Spidybot]

Re: What is an anti-syphon valve?

Not knowing your tank design (std. transportable or built in) I can't give you a 100% answer. Your tank does need some kind of controlled 'breathe' to allow fuel used to be replaced by air.<br /><br />Anti-syphon and vent is OK as long as it does not allow air to get into the fuel supply line. <br /><br />Such items belongs to a separate vent line and/or the the filling hose/stud/cap (if you have a built in tank).<br /><br />Your bulb should, under all circumstances, stay hard until your motor runs. The valve(s) in the bulb are designed to cope with this. Not that it would keep for hours but easily for time you need to start up.<br /><br />Ask again if still in doubt.

 

[rickdb1boat]

Re: What is an anti-syphon valve?

OK UU, I have a Pontoon with a Built-in Poly Tank. I had to remove the tank to clean it because of water contamination. When I removed the Tank, I also removed the fuel sending unit and the the Pick-Up assembly as well. Well the Tank had all kinds of gook in in. So I cleaned it well, also found a small spring and washer laying in the bottom of the tank. Assumed this was part of the built-in Anti-Syphon Valve "IN" the Tank Pick-up assembly, not the Bulb. I have heard that others have removed this Valve, as it has caused problems! So, what I need to know is: Do I need this Anti-Syphon Valve IN the Tank Pick-up assembly? As I said, when I squeeze the Primer Bulb, it will become firm after a few pumps and then it starts to push fuel BACK into the Tank. Is this Normal? If not, what do I do? Whew, And I thought this would be question that even I should know! I know, promised no more questions on this, BUT!! Thanks for the replys!

 

[Spidybot]

Re: What is an anti-syphon valve?

Let's get the facts out:<br /><br />You need a new bulb as this prevents the pushing back.<br /><br />You can remove the parts left here and there as long as the tank has sufficient ventilation.

 

[rickdb1boat]

Re: What is an anti-syphon valve?

Thanks and I'm Done! Will get new bulb! Appreciate you help!

 

[Bear]

Re: What is an anti-syphon valve?

just a link:<br /> http://marinemechanic.com/asof-8-29/antsiphon.htm <br />

 

[rickdb1boat]

Re: What is an anti-syphon valve?

Thanks Bear, I'm still working on it!