Originally Posted by
neurocop
They also get hot from the friction of the piston gasket rubbing the pump chamber tube (they will heat up less if you take your time and pump slowly).
Not exactly. Air heats up as it's compressed and cools as it expands. The pump gets hot from some of the work done compressing the air. If you have an air compressor, you might have noticed how hot the line from the compressor to the tank gets.
http://en.wikipedia.org/wiki/Charles%27s_law