A reciprocating atmosphere compressor is a Piston Air Compressor positive displacement compressor that uses a crankshaft-driven piston and cylinder to compress the atmosphere. … A two-stage compressor contains an additional step where in fact the air is compressed by another, smaller piston to a pressure of up to 175 PSI.

Like a small internal combustion engine, a conventional piston compressor has 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 at atmospheric pressure to drive open the inlet valve and fill up the region above the piston.