A reciprocating air flow compressor is a positive displacement compressor that uses a crankshaft-driven piston and cylinder to compress the atmosphere. … A two-stage compressor contains an additional step where the atmosphere is compressed by another, Piston Air Compressor smaller piston to 
a pressure of up to 175 PSI.
Like a little internal combustion engine, a typical piston compressor includes a crankshaft, a connecting rod and piston, a cylinder and a valve head. … As the piston techniques down, a vacuum is established above it. This allows outside air flow at atmospheric pressure to force open the inlet valve and fill up the region above the piston.