I am reading a lot of fuel related threads and see reference to an 'anti-siphon valve'. Could someone I know I'll get many please explain : 1. What they are. How they work. Why they are required. I don't have anything in the line between the fuel end of the pickup in my tank and the engine mounted primary water separating fuel filter Thanks again, Chris Joined Oct 17, Messages Re: 'Anti-siphon valve' - Please explain It is a valve in your fuel line that stops fuel from siphoning back to your fuel tank.
When you shut down ball seals again this prevents you from having to pump bulb every time you start up. Your primer bulb also has one in it.
They should be checked every now and again if they stick they can limit the amount of fuel to carbs and lower your RPM at wot. Don S Honorary Moderator Emeritus. Joined Aug 31, Messages 62, Re: 'Anti-siphon valve' - Please explain The anti siphon valve has one purpose. It prevents fuel from siphoning out of the gas tank incase the hose is cut or burned off at some point and hangs below the level of fuel in the tank.
Which would cause the gasoline to siphon out of the tank. Hence the name anti siphon valve. It's normal location in US boats is the hose barb fitting that is screwed into the fuel pickup tube coming out of the fuel tank. They are either aluminum or brass, and look just like a hose barb fitting, except the have a check ball and spring in them. Many people mistakenly think they are there to prevent fuel from flowing back into the fuel tank when the engine is not running.
That is done by the fuel pump, not the anti siphon valve. Re: 'Anti-siphon valve' - Please explain Don S said:. The anti siphon valve has one purpose. Click to expand Re: 'Anti-siphon valve' - Please explain It takes about 1.
This is above what a siphon can cause, but well below what a fuel pump will pull. Re: 'Anti-siphon valve' - Please explain Thanks Don. Joined Dec 8, Messages 10, Re: 'Anti-siphon valve' - Please explain The operative word here is "Siphon" The fuel can siphon if any part of the fuel line from the tank runs below the fuel level of the tank.
With this arrangement, you don't worry about the valve hanging up. The vented passage is always open. And you can easily tell when the water is running and when it stops. This flow, however, must not be of such volume that it adversely affects the cooling of the exhaust.
Flushing regular doses of vinegar through the head will help to diminish any deposits. His depth of technical knowledge comes from living aboard various boats with his family for more than 30 years, cruising far and wide, and essentially learning how to install, fix, and rebuild every system onboard himself.
A lawyer by training, for most of his career Tom has been an editor and columnist at national magazines such as Cruising World, PassageMaker, and Soundings.
These days, Tom and his wife Mel enjoy cruising their Camano 41 Chez Nous with their grandchildren. We use cookies to enhance your visit to our website and to improve your experience. Membership Search. Service Locator. Get a Quote. Become a Member. Renew Membership. Boat Insurance Membership Boat Towing. Boat Insurance. Boat Towing. Membership Plans Savings. Boat Show Tickets. Boat Lettering. Boat Loans. Vessel Documentation FAQ. Maintenance Techniques Tow Vehicles.
How-To DIY. Cleaning Exterior Systems. Electronics Equipment Maintenance Techniques. Call For a Tow Also be careful if you decide to check the fuel pickup line, if you mess up that connection it's not going to a fun fix. Will do. Very Helpfu! One more thing I get that if a gas tank is not fully ventilated in will cause gas starvation.
How can a faultly anti-syphon valve do the same? Hi The vent does 2 things let's fumes go helps regulate the fuel flow preventing starvation as you identified The anti-siphon valve stops fuel from sucking back towards tank. Damn Valve! Here's a nice snip that sums up nicely this link may help others too ""If the fuel tank cannot breath, it will cause a reverse suction condition and prevent fuel from getting to the motor.
Last edited by a moderator: Jul 10, I sense a moderator may tell me I made a boo boo. Joined Aug 21, Messages 9. The anti-siphon valve is very similar to a simple check valve. This could cause a fire or continue to feed a fire by dumping fuel when the engine is off. It is especially a concern on larger boats where the fuel tank may be mounted higher than the fuel inlet to the carburetor, which would allow a siphon to start easily.
The fitting itself has a spring and ball bearing. When the engine is running, the fuel pump suction overcomes the spring force, and pulls fuel past the ball bearing. When the engine is off, the spring and ball bearing prevent fuel from siphoning out of the tank, and stops fuel in the line from emptying back into the tank helps to keep lines full of fuel If this fitting gets corroded, the ball bearing may stick, and prevent adequate fuel flow.
Joined Jul 7, Messages 14,
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