Probably the kinetic energy of rubbing the pump against the valve, combined with the increase in gas pressure in the tire itself.
The acid and alkali that would react to make sodium sulfate is
alkali= sodium hydroxide
acid = sulphuric acid
<u><em>explanation</em></u>
Acid react react with alkali to form salt and water.
For sodium sulfate salt to be formed a sulfate acid is required to react with a hydroxide of sodium .
therefore Sodium hydroxide (alkali) react with sulphuric acid (an acid) to form sodium sulfate (salt) and water.