Avid bicyclists know that keeping tires inflated can be a chore if you have a slow leak. Ride to work in the morning and your tire might be fine and then it’s flat when you are ready to ride home in the evening. An inventor called Benjamin Krempel has invented an intertube called the PumpTube that inflates itself as you ride.
PumpTube has a one-way valve that is attached to the valve stem that draws air in from the atmosphere to the inside of the tire. That air doesn’t go directly into the inner tube though; it is sucked into one end of a pumping mechanism that is essentially a tube inside the tire. That tube runs along the outside of the main inner tube of the tire.
As the wheel rolls along the ground, the pumping mechanism is compressed and forces air into the inner tube of the tire. When the air is forced out of the pumping mechanism into the inner tube, a vacuum is created that draws more air in from the atmosphere.
The fancy valve stem can be set at a pressure that the rider wants and when the tire is at that pressure, no more air is drawn into the tire. The pressure desired is set directly on the valve stem. The PumpTube will sell for $30 to $55 each and the designer hopes to raise money on Kickstarter next year. This sounds like a system that should be adapted to cars to keep tires filled at the correct pressure.