in a research project at the royal institute of technology we have developed a pump based on a new fluid pump principle with no valves. the pump consists of two fluid flow rectifying diffuser/nozzle elements which are connected to the inlet and outlet of a pump chamber with an oscillating pump diaphragm, as shown in fig.1.

the diffuser/nozzle element has a lower flow resistance in the diffuser direction (indicated by the larger arrow), i.e. in the direction of increasing cross-sectional area, than in the opposite nozzle direction (indicated by the smaller arrow). this means that the diaphragm oscillation results in a new flow in the diffuser direction. both conical and flat-walled diffuser/nozzle elements can be used.

fig. 1. the principal operation of a valveless single-diaphragm pump
during the supply and pump modes.

a pump with two pump elements in parallel is shown in fig.2. the pump cavities and diffusers are milled in two 0.5mm thick brass plates which are glued together. the four diaphragms (two per pump) are driven by piezoelectric discs. the pump has a maximum volume flow of 16 ml/min and a maximum pump pressure of 1.7m h₂o.

the pump was operated at the pump resonance frequency of 540hz, which results in a maximum diffuser throat velocity of 16 m/s. we have also fabricated an electromagnetically driven larger pump with a pump flow capacity of 1.8 litres/min and a smaller pump based on silicon micromachining. recently we have developed a gas pump based on the same valveless pump principle.

fig. 2. a top and side view of the design of a valveless two-chamber
pump with four diaphragms.

the pump arrangement with no moving parts has several advantages, including very high reliability and long lifetime. furthermore, the simple structure facilitates small size and low fabrication costs. since we believe that these characteristics make the pump ideal for use in reliable and compact liquid cooling systems of electronics, we are currently developing a small sized pump prototype with target specifications of 120 ml/min at 0.1m h₂o. the pump is intended to be used in a cooling application where the coolant is water.

erik stemme and göran stemme
department of signals, sensors and systems
royal institute of technology
stockholm, sweden