How a Bicycle Pump Works

Bicycle pumps are used to inflate bike tires. Pump performance can be described in two ways: the action of pump parts during inflation or the changes in volume and air pressure that occur within the pump during its use.

  1. Bicycle Pump Parts

    • A bicycle pump is a hollow cylinder containing a plunger, or piston. A piston rod connects the piston to a handle outside the cylinder. Two one-way valves, an intake valve built into the piston and an outlet valve at the bottom of the cylinder, ensure unidirectional air flow. A hose connects the outlet valve to a tire valve nozzle.

    Pump Action

    • Moving the bicycle pump piston up and down within the cylinder traps air and delivers it to the tire. Pulling the piston upward draws air into the cylinder through the piston intake valve. Depressing the piston forces the air trapped within the cylinder through the outlet valve, hose, hose nozzle and tire valve, thereby inflating the tire.

    Volume and Pressure

    • Moving the pump piston up and down changes the volume, or available air space, within the cylinder. According to Gears Educational Systems, depressing the pump piston decreases cylinder volume and increases internal air pressure. When air pressure within the pump exceeds tire pressure, air enters the tire. Pulling the piston upward increases cylinder volume and decreases internal air pressure relative to that of the external atmosphere. External air is sucked into the cylinder to equalize the pressure difference.