A Schrader valve is a type of gateway that allows air to be pumped into a car tire or other pressurized object. Present on just about all cars and trucks on the road, the Schrader valve protrudes from the rim of the wheel, and a pump can be attached to it. The pump presses against a pin inside the valve, which opens the chamber to allow air to pass through. When the pump is removed, the spring-loaded pin closes, sealing off the air inside the tire. A Schrader valve is often fitted with a plastic cap when not in use to prevent dirt and moisture from clogging the valve.
While the Schrader valve is present on just about all motor vehicle tires and rims, it is only present on some bicycle tires and rims. Bicycle tires and rims are often quite narrow, meaning a drilled opening for a Schrader valve would be too wide and could weaken the rim. A Presta valve is often used in place of the Schrader valve. The Presta valve is much narrower than the Schrader valve, and it seals off the chamber using just the pressure inside the tire or inner tube, unlike Schrader valves, which are sealed off by a spring loaded pin.