Fuel Systems

Manufacturer Requirements

"Anti-siphon protection” is a term applied to the means of preventing the siphon action of permitting fuel to continue to flow out of the fuel tank in the event there is a break or rupture in a fuel distribution line, or if a fitting in the fuel line loosens, creating a leak.

"Anti-siphon protection” may be accomplished by one or more of the following methods:

(a) Keep all parts of the fuel line from the fuel tank to the fuel line connection at the carburetor above the level of the top of the fuel tank. The tank top level is determined with the boat in its “static floating position.” Practically, the fuel pump and fuel filter(s) must also be above the tank top.

(b) Install an anti-siphon device at the tank withdrawal fitting. The fuel distribution line may then run below the level of the tank top. A filter may be installed between the fuel tank withdrawal fitting and the anti-siphon device.

NOTES:

1. Some anti-siphon devices are spring loaded check valves. These valves have a specific cracking pressure and provide protection up to a specific head. Therefore, the anti-siphon valve must be selected or ordered to protect against the siphon head for a particular installation.
2. Too high a cracking pressure may cause vapor lock. This has become an increasing problem with reformulated gasoline (RFG). Be sure to select the correct cracking pressure.
3. Some anti-siphon devices involve a bleed hole in the fuel pick-up tube, near the top of the fuel tank. The size of the hose is critical for a particular application. Each installation using this type of protection must be evaluated to assure its effectiveness. Too large a hole will bleed excessive air into the fuel flow effecting engine operation. Too small a hole may not stop fuel flow in the event of a fuel leak. This installation is used very infrequently because of inherent problems that may result.

(c) Install an anti-siphon device at a location where a line from the fuel tank will no longer remain above the fuel tank top level. The anti-siphon device will then protect the portion of the line that must run below the tank top level. The portion of the line that is above the fuel tank top level will be automatically taken care of.

(d) Install an electrically operated fuel stop valve at the fuel tank withdrawal fitting. This valve requires electrical power to open and must be connected to operate only when the ignition switch is on. A filter may be installed between this valve and the fuel tank withdrawal fitting. Electrically operated fuel stop valves must comply with 183.528.

(e) Install an electrically operated fuel stop valve at the point in a fuel line where it must run lower than the fuel tank top level. This valve requires electrical power to open and must be connected to operate only when the ignition switch of the engine it serves is on. A filter may be installed between this valve and the fuel tank withdrawal fitting. Electrically operated fuel stop valves must comply with 183.528.

NOTES:

1. Fuel stop valves used in the fuel system, whether electrically operated or manually operated, must withstand the 2-1/2 minute fire test in accordance with 183.590.
2. Anti-siphon devices are not required to meet a fire test.
3. The fuel stop valve is required to be directly at the fuel tank connection by 183.568(c)(1) and must be installed so that it can be operated from outside the compartment. This can be accomplished with a reach rod or a long valve stem. The installation of an access panel over the valve is also permitted. However, once open, the valve must be immediately accessible inside the panel so that the operator does not have to reach through fire to shut off the fuel.

FIGURE 34 - Anti-Siphon Protection

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