Fluidic Diode

So simple. So effective.

A fluidic diode is a passive device that has a lower flow resistance in the preferred direction than in the opposite direction. Simply put, it means that a fluidic diode has very low resistance in one direction and, depending on the design, very high resistance in the opposite direction. This can be used, for example, to prevent a flow from striking back. The principle generally works independently of the medium, be it a liquid or a gas.
The basic idea was patented by Nikola Tesla in 1916 and is based on flow obstacles that create a rather laminar flow in the preferred direction and strong turbulence in the opposite direction. The great advantage of such a component is that these valves do not have any moving parts, react very quickly and are therefore virtually maintenance-free. The disadvantage of the components is that they do not completely stop the backflow, but only slow down the reverse flow significantly. Further details, which we are unfortunately not allowed to show here for legal reasons, can be found in the publications we have listed at the end of this page.

The picture shows the original “Tesla Valve” from Nikola Tesla’s patent 1916. When the current flows through the component from the right side, the diode shows low resistance. If, on the other hand, the fluid flows through the diode from the other direction, the fluid is conducted through the side channels, which massively increases the flow resistance.

Non-return valve in a gas turbine. An application example.

In internal combustion engines, such as gas turbines, a flame blowback against the main flow direction not only brings the combustion process to a standstill, but can also cause severe damage to and in the engine. In order to ensure a non-return operation, FDX has developed a non-return valve based on the principle of a fluidic diode. The diode was designed for highly reactive mixtures (air with dimethyl ether). In contrast to the test diode, the diode developed by FDX has a higher resistance ratio of preferred and opposite direction. This means that the pressure loss in the preferred direction is particularly low and there is also a high resistance in the opposite direction. The diode developed by FDX has proven to be absolutely reliable in combustion tests and will be used in the next generation of gas turbines. The following video illustrates once again how it works. If you are interested or have any questions, please do not hesitate to ask us, we will be happy to advise you.

Application. Characteristics.

There are numerous designs of fluidic diodes, some of which can also have a very high relative pressure drop in the blocking direction. However, most of them also have in common that they generally have a high pressure drop or are difficult to manufacture. The diode developed by FDX was designed for a particularly low pressure drop in the main flow direction. The relative pressure loss in the blocking direction is greater by a factor of 20, but can be adjusted as required. In addition, the shock wave can be focused in the shut-off direction, making the diode ideally suited as a non-return valve, and not only with liquids but also with gases.

In addition, the components can also be used as pressure shock absorbers. When a valve (e.g. a water tap) is closed, a shock wave is generated which runs against the direction of flow. The strength of the shock wave depends largely on how fast the valve is closed and can sometimes cause considerable damage in pipes and pumps. The fluidic diode can help here by being integrated into the line between the pump and the valve. The return shock wave is significantly weakened by the diode, so that it can no longer cause any damage. Since no moving parts are used, the components are maintenance-free and shine with very fast reaction times, which a mechanical system cannot achieve due to its principle.

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pressure shock

highly reactive

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Links. References.

  • P. J. Baker. A comparison of fluid diodes. In Proceedings of the 2nd Cranfield Fluidics Conference, 1967
  • J. M. Kirshner and S. Katz. Design Theory of Fluidic Components. Academic Press In., 1975. ISBN 978-0124102507.