A reciprocating air compressor is a positive displacement compressor that uses a crankshaft-driven piston and cylinder to compress the air. … A two-stage compressor includes an additional step where the air is compressed by a second, 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 moves down, a vacuum is created above it. This allows outside air at atmospheric pressure to push open the inlet valve and fill the area above the piston.