A bicycle air pump will not only inflate a bike tire, but will inflate automobile tires, utility tires or even sports equipment such as a football as long as the correct air transfer valve fittings are used. Unlike a large volume air pump for automobile or general usage, a bicyclist needs a lower volume of air pumped to a higher pressure to inflate a bicycle tire. While most manual pumps work on the same principle, special needs with bicycle pumps are portability, light weight and ease of use.
Principle
Bicycle tire pumps transfer air from an atmospheric pressure of 14.7 lbs. per square inch on the intake stroke to the higher pressure desired in a bike tire, usually between 40 and 60 psi. Higher pressures, over 100 psi, are used in narrow racing tires. The number of strokes needed to fill a bicycle tire depend on the volume of the pump chamber, the pressure needed in the tire and size of the bicycle tire being inflated. The air is transferred through a rubber hose with a fitting which can be snap-fitted to the tire valve to leave your hands free to operate the pump.
System
A manually powered bicycle tire pump brings air into a cylinder chamber as a piston pulls outside air into the chamber on the "up" stroke of the pump cycle. Raising the piston handle up opens a valve to the outside air while the valve opening to the tire is closed. On the push or "down" stroke, the valve to the outside air closes and the valve leading to the hose of air going to the tire opens. As the pump handle is pushed, the piston also compresses the air and forces it into the tire tube. This increases the pressure so the tire inflates and holds weight. The higher the pressure, the less rolling resistance for pedaling.
Types
A portable air canister with enough air to inflate a bicycle tire can be carried easily on a bike, but is only good for single usage. Manual bicycle pumps come in a variety of configurations, from larger, less portable models, with fixed hand and foot handles and a built-in pressure gauge to more portable units with folding hand and foot pegs that can be snapped to the bicycle frame. Bicycle tire air valves must be the same type as the air pump (Schrader or Presta) or the bicycle air pump must have an adapter.
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