Reciprocating positive displacement pumps are really important machines in lots of industries. They move liquids using this back-and-forth motion, you know like a bicycle screw pump. When you push it down air goes in the tire, and when pull up it sucks more air. These pumps does similar thing with pistons moving up down or back forth to push the liquid through pipes. You can find them often in oil refineries, chemical plants or water treatment places. Shanghai Changlong makes this kind of pumps, they make sure its reliable and works efficient for different uses.