Wet the valve with soapy water or saliva. If an air bubble forms, tighten the valve tightly using the inverted dust cap.
Note: The valve can only be tightened with a metal cap. Such metal caps can be purchased at petrol stations.
Check the valve again. If air bubbles still form and the valve no longer tightens, it must be replaced.
Be sure to reattach the dust cap to the valve.
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