Liquid tank venting system

1. A fuel tank equipped with a liquid tank venting system comprising:

a chamber that is inside the fuel tank and that is equipped with a drainage device, the drainage device including

at least one draining opening made in the chamber, and

a non-return valve including an elastomeric part, the non-return valve being capable of sealing/freeing the draining opening; and

at least one vent valve including a vent float,

wherein the non-return valve is forced into a position for leaktight closure of the draining opening via the vent valve starting from a certain liquid level in the fuel tank,

wherein the elastomeric part of the non-return valve is one of an umbrella valve or a duck bill valve,

wherein the non-return valve is located on a perimeter of the draining opening in the chamber,

wherein said non-return valve comprises at least one part that is deformable when a weight of liquid present in the chamber is applied thereon, such that when the at least one part is deformed, the draining opening is free,

wherein the vent float of the vent valve is a closure float that moves as a function of the liquid level in the fuel tank and that acts directly or indirectly on the elastomeric part of the valve,

wherein the non-return valve is an umbrella valve, and

wherein the vent valve further includes

a lever arm activated by the closure float, and

at least one excrescence or support that exerts pressure on an edge of the umbrella valve starting from the certain liquid level in the fuel tank.

2. The fuel tank according to claim 1 , wherein the non-return valve is located under the chamber or in an extension of the chamber, and

wherein the vent float is a preloaded float having the elastomeric part of the non-return valve attached to an upper part thereof, the elastomeric part sealing the draining opening in the chamber depending on the liquid level in the fuel tank.

3. The fuel tank according to claim 1 , wherein the vent float is an annular float including an annular apex, a size and position of the apex being such that the apex presses on an edge of the umbrella valve in a top position of the float, said float sliding into an excrescence of the chamber that is open at a bottom portion of the chamber.

4. The fuel tank according to claim 1 , wherein the vent valve is separate from the chamber and connected to the chamber by a ventilation duct.

5. The fuel tank according to claim 1 , wherein the vent valve is integrated into the chamber.