Anti-siphon Valve

[Rangerwing]

I recently had a mechanic remove my anti-siphon valve to eliminate a fuel starvation issue. Not having much time I picked up the boat and wasn't able to speak with the mechanic. I have a friend who needs to remove two anti-siphon valves from his tanks on his older Ranger, but neither of us are savvy on how to get to it (not wanting to trash the system due to ignorance).

Anyone out there willing to pass on tips,pointers or step-by-step instructions on going about this? It has to be a fairly simple task, but would like to eliminate excessive spending is possible.

Thanks,
Rangerwing in OKC

 

[emdsapmgr]

Re: Anti-siphon Valve

It's pretty easy. Most anti-siphon valves are disguised as the hose barb that screws into the fuel pickup on the top of the built-in fuel tank. Unscrew it and replace it with a similar brass fuel barb-which has no valve. When you get the old valve out, you can see a chrome ball valve in the end. Make sure you get the new fuel barb that is large enough to flow the proper amount of fuel to feed your engine.

 

[Joe Reeves]

Re: Anti-siphon Valve

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

 

[MikDee]

Re: Anti-siphon Valve

Decided to include Quote from previous poster, see my next post.

 

[Chris1956]

Re: Anti-siphon Valve

Sometimes you can drive the ball out of the hose barb with a nail and hammer.

 

[MikDee]

Re: Anti-siphon Valve

It's pretty easy. Most anti-siphon valves are disguised as the hose barb that screws into the fuel pickup on the top of the built-in fuel tank. Unscrew it and replace it with a similar brass fuel barb-which has no valve. When you get the old valve out, you can see a chrome ball valve in the end. Make sure you get the new fuel barb that is large enough to flow the proper amount of fuel to feed your engine.

Not a good idea, as it is required by the Coast Guard! One function it has is to keep fuel from leaving the tank if you have a leak somewhere, so the fuel doesn't siphon out into your bilge for any reason, hitting the ignition will make it go boom! Or, if the boat capsizes, it helps keep the fuel contained in the tank. Just replace it if needed

 

[ezeke]

Re: Anti-siphon Valve

Coast Guard regulation does not require the anti-siphon valve if the tank is lower than all of the fuel connections and the engine.

The anti-siphon valve will not prevent backflow to the tank.

 

[Rangerwing]

Re: Anti-siphon Valve

I've got both pros and cons on having a functioning valve. I will probably install a new one soon - however, I need to positively identify the exact location of the valve. Is it the horizontal fitting that tees off the fitting on the top of the tank? Is the valve between the tank and the outflow hose? Is the thing INSIDE the tank? I don't see an easy way of opening the tank by way of the fuel line pickup tube - it seems to be sealed at the top of the tank.

All the replies and advice is greatly appreciated!

Thanks,
Rangerwing
OKC

 

[ezeke]

Re: Anti-siphon Valve

It is usually in the first removable metal fitting leaving the tank and almost always consists of a spring and a stainless steel ball that can be knocked out of the fitting.

 

[emdsapmgr]

Re: Anti-siphon Valve

I had problems with mine at high rpm (high fuel flow.) When I autopsied the valve, there were a few grains of really fine sand between the ball and the housing, causing it to stick partially open. Not so sure that a good cleaning with some carb cleaner might not have fixed the problem. That's why I don't run them anymore.

 

[Rangerwing]

Re: Anti-siphon Valve

Thanks guys,

My original issue was stalling out during transition from idle to full power. I'd often have to toy with the choke during this period and usually get lucky enough to get her up on plane. Once there, she seems to be able to run great all day. Once at idle for a moment, the whole frustrating process would repeat itself.

Because I had to use the choke I assumed the problem was the carbs. I run a Johnson 150 Fast Strike V6 with as many carbs. I was told by several the low speed jets could be the source of my problems. Sounded plausible except the primer bulb was going flat.

Once the mechanic tested the engine, electronics and anything else usually done during the preliminaries, he narrowed it down to the anti-siphon valve. He didn't replace it, just removed it, claiming my boat didn't need it, and that I'd be surprised to learn just how many run without one. Never knew they existed until lately.

I'll pass on all the advice to my friend and chock what I've learned here to valuable information. I sure do thank you guys for all the help.

Salute!
Rangerwing
OKC

 

[MikDee]

Re: Anti-siphon Valve

Coast Guard regulation does not require the anti-siphon valve if the tank is lower than all of the fuel connections and the engine.

The anti-siphon valve will not prevent backflow to the tank.

Then why is it on every boat? is it a federal reg? and being a spring loaded check valve (one way valve) and me being a pipefitter, how can you say it won't prevent backflow to the fuel tank? I'm curious, educate me if you will

 

[Silvertip]

Re: Anti-siphon Valve

The valve unseats when the engine is running. It requires very little negative pressure (suction) to unseat. However if you were to hang the fuel line over the side of the boat with the end below the fuel level in the tank, without the valve you would have a siphon action. But with the valve, the valve will not unseat so siphon cannot happen. If the end of the hose were about 10 feet or so below fuel level and you actually got a siphon action going, then yes, it would unseat but flow would be slow. Inside the boat there is no way siphon can happen with a properly functioning valve. It is a common misconception that the purpose of the valve is to prevent backflow from the engine to the tank. That is simply not the case as any pressure build up in the line can unseat the valve the fuel will flow backwards. The valve looks like this one:

 

[ezeke]

Re: Anti-siphon Valve

Then why is it on every boat? is it a federal reg? and being a spring loaded check valve (one way valve) and me being a pipefitter, how can you say it won't prevent backflow to the fuel tank? I'm curious, educate me if you will

It's a boat manufacturers' regulation, not a engine manufacturers'. So the boat builders put them on the tanks that they install. But, notice the word or in (a)

The regulation is CFR
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.​

 

[MikDee]

Re: Anti-siphon Valve

The valve unseats when the engine is running. It requires very little negative pressure (suction) to unseat.

True, the spring is weak

However if you were to hang the fuel line over the side of the boat with the end below the fuel level in the tank, without the valve you would have a siphon action. But with the valve, the valve will not unseat so siphon cannot happen.

True because the spring is on the back side (outward side of the check ball) not letting it open to siphon.

If the end of the hose were about 10 feet or so below fuel level and you actually got a siphon action going, then yes, it would unseat but flow would be slow.

True, it would over come the light spring pressure

Inside the boat there is no way siphon can happen with a properly functioning valve.

True

It is a common misconception that the purpose of the valve is to prevent backflow from the engine to the tank. That is simply not the case as any pressure build up in the line can unseat the valve the fuel will flow backwards.

False, if the ball check is now sealed snugly against it's machined seat (not the spring side), it will not let any amount of pressure unseat it, Unless there was pressure built up in the fuel tank, unseating the valve from the spring pressure side

The valve looks like this one:

Or it could look like an angled tank fitting as well.

[/QUOTE]

 

[ezeke]

Re: Anti-siphon Valve

The test for a properly functioning anti-siphon valve is that it will hold a column of water 36" long. It should not hold a column of water longer than that and siphoning should occur.

The regulations do not require that an anti-siphon valve should prevent backflow.

 

[MikDee]

Re: Anti-siphon Valve

The test for a properly functioning anti-siphon valve is that it will hold a column of water 36" long. It should not hold a column of water longer than that and siphoning should occur.

The regulations do not require that an anti-siphon valve should prevent backflow.

Ah, But it does by design, it is in essence, a one way valve.

From Wikipedia: "A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, many check valves are very small, simple, and/or cheap. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal

A ball check valve is a check valve in which the disc, the movable part to block the flow, is a spherical ball. In some (but not all) ball check valves, the ball is spring-loaded to help keep it shut."