Oh Ye Wise Prius Techies out there... I've heard numerous references to the bladder in the gas tank, but have no idea what it is or what it does. What's the purpose of it? Any idea what it's made of?

I hardly qualify, but that won't stop me from answering. The gas tank has some sort of expandable liner which expands as you pump gas in and contracts as the gas is used. The point is to reduce the amount of vaporized gasoline that the system has to deal with.<br><br>Consider: In a traditional gas tank, when you fill up, the air that the incoming gas displaces is saturated with gasoline fumes. It comes out of the filler nozzle in part and and in part is dealt with by some internal systems. With a bladder, the air that is displaced is on the other side of the bladder and has little if any gas fumes in it.<br><br>What I have a hard time understand is what prevents the gas from blowing back in your face as you pump it in. Presumably the bladder is not like a balloon, but more like a float.<br><br>The NCF book mentioned what it was made of, but I don't remember. Not rubber or neoprene.<br><br>Burns

"What I have a hard time understand is what prevents the gas from blowing back in your face as you pump it in."<br><br>With a balloon, the pressure inside is greater than the outside (once inflated to the point the rubber starts to stretch) so the natural tendency is to reach equilibrium (deflate). It is the same with the bladder, the inside and outside pressure is basically the same, UNTIL you cause the bladder to stretch (overfill) then the same thing will happen and you will be spewed with gas as some of the early adopters learned when they tried to stretch out their gas station visits a little more. :)

Yes. What I don't understand is this: The bladder must expand and contract in order for it to do any good (i.e. the goal is to prevent there from being any air space above the gasoline in the tank). So it must be made of a very interesting material which contracts when the gas is extracted, but which does not have enough strength of contraction to expel gas except when it is extremely full.<br><br>Burns

It's like a water bed mattress. The shape of the bag is the maximum size of the frame. It's just flexible so when less is in the tank it flexes and folds over. I understand the bladders help prevent gas from leaking out the tank if the tank is damaged in a accident.

It is made of the same plastic material used by some manufacturers for gas tanks, only thinner. Think of it as a plastic tank within a steel tank. As others have stated, the purpose is to reduce the volume of fuel vapor by expanding and contracting the fuel storage space. Think of it as a heay duty Playtex Nurser!<br><br>Dave

It's a four or five layer coextrusion.<br><br>I searched and searched but have yet to find the article. It was in Modern Plastics or Design news, i forget which.<br><br>'Twas one of the articles that turned me on to the Prius, in the "before-time."<br><br>Jeff