What keeps air from leaking from a basketball?

What keeps air from leaking from a basketball?
Nearly all basketballs have an inflatable inner rubber bladder, normally wrapped in layers of fiber and then covered with a tacky surface made either from leather (traditional), rubber, or a synthetic composite. As with most inflatable balls, there is a small valve similar to that used onpneumatic tyres to allow the pressure to be increased or decreased. The inside pressure of the air pushes the inner section of the value against a seal. If the ball required deflating to meet game regulations the inner valve is pushed in breaking the seal and releases air under pressure. When the inner value is release it is forced back in to position by the air pressure inside the ball. When inflating a mechanism inside the pump pushes the inner valve down, however, the air cannot escape because the pump connections forms a seal. When pressure is placed on the pump (pumping up) air is forced in to the ball. When the pump mechanism is removed there is a small escape of air from the ball as the inner valve raises up and again forms a seal.