Valveless pumping is currently used in assisting the transportation of fluids in both biomedical and engineering systems. Whether it be to imitate the body's transport methods in medicine, or to pump ink onto paper, there are no valves present to regulate flow direction. Many systems in nature and engineering more or less rely upon valveless pumping to transport fluids, such as blood circulation being maintained to an extent even when the heart’s valves fail. Additionally, the heart of an unborn baby begins pumping blood long before the development of discernible chambers and valves. This process is now known as the 'Piezoelectric' process.
Piezoelectricity is the electric charge that accumulates in certain solid materials (such as crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical stress. The word 'piezoelectricity' means electricity resulting from pressure.
The first recorded observation of capillary action was by Leonardo da Vinci, and Albert Einstein's first paper, which was submitted to Annalen der Physik in 1900, was on capillarity. In 1660, capillary action was still to be officially discovered by the Irish chemist Robert Boyle. Boyle reported an experiment in which he dipped a capillary tube into red wine and then subjected the tube to a partial vacuum. He found that the vacuum had no observable effect on the height of the liquid in the capillary, so he concluded that the behavior of the liquids in capillary tubes was due to a process different than that which influenced mercury barometers.
Valveless impedance pumps
In microfluidics (a multidisciplinary field intersecting engineering, physics, chemistry, biochemistry, nanotechnology, and biotechnology, with practical applications to the design of systems in which small volumes of fluids will be handled.), valveless impedance pumps have been fabricated, and are expected particularly suitable for handling sensitive biofluids. An impedance pump is a valveless pump consisting of an elastic tube connected on both ends to an inelastic tube. Tapping the end of a tube will cause flow of liquid inside the system. Typically fluids are moved, mixed, separated or otherwise processed this way. Numerous applications employ passive fluid control techniques, like capillary forces.
Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of, and in opposition to, external forces like gravity. In Robert Boyle's experiment, this would be the ability of the red wine to flow through the capillary, working upwards against gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper, in some non-porous materials such as liquified carbon fiber, or in a cell. It occurs because of intermolecular forces between the liquid and surrounding solid surfaces. The capillary action is therefore due to the pressure of cohesion and adhesion which cause the liquid to work against gravity.
To date, the most successful commercial application of microfluidics is the inkjet printhead. Ink jet printers operate on this same principal using valveless pumping. The pump chamber is emptied through the printing jet due to reduced flow impedance in that direction and refilled by capillary action.