Editing Pump (section)

===Valveless pumps===
Valveless pumping assists in fluid transport in various biomedical and engineering systems. In  a valveless pumping system, no valves (or physical occlusions) are present to regulate the flow direction.  The fluid pumping efficiency of a valveless system, however, is not necessarily lower than that having valves. In fact, many fluid-dynamical systems in nature and engineering more or less rely upon valveless pumping to transport the working fluids therein. For instance, blood circulation in the cardiovascular system is maintained to some extent even when the heart's valves fail. Meanwhile, the embryonic vertebrate heart begins pumping blood long before the development of discernible chambers and valves. Similar to blood circulation in one direction, [[Bird_anatomy#Respiratory_system|bird respiratory systems]] pump air in one direction in rigid lungs, but without any physiological valve. In [[microfluidics]], valveless [[impedance pump]]s have been fabricated, and are expected to be particularly suitable for handling sensitive biofluids. Ink jet printers operating on the [[Piezoelectricity#Actuators|piezoelectric transducer]] principle also use valveless pumping. The pump chamber is emptied through the printing jet due to reduced flow impedance in that direction and refilled by [[capillary action]].