Valve Design Employs Umbrella-Flipping Phenomenon
On a windy day, an umbrella can flip inside out—an irritating phenomenon that researchers have now used in the design of a fluid-control valve. The team developed a theory for the motion and tested it in experiments. The valve can snap open or closed without requiring the extra energy that is normally needed to actuate a valve [1]. This fluid-regulation concept may have uses in wearable devices, microfluidics, or soft robotics.
An umbrella has two stable states. When enough pressure builds up underneath the canopy (typically from wind), the umbrella quickly shifts from one state to the other. This process is called a snap through, and similar phenomena occur in systems such as carnivorous plants like bladderworts and jumping children’s toys.
Matteo Pezzulla, a mechanical engineer at Aarhus University in Denmark, and his colleagues wanted to know if this effect could be used to design a new type of valve that would be passive—not triggered by any external components. Previously designed passive valves have reduced complexity and energy consumption, says Kaare Jensen, a soft-matter biophysicist at the Technical University of Denmark. “Passive controllers are probably a better way to manage fluid flows, instead of using motorized valves and similar power-hungry devices.” The team wanted a valve that also “exploits snapping to suddenly cut off the flow to specific channels,” Pezzulla says.
A flexible, dome-shaped membrane could be positioned near the end of a narrow pipe surrounded by a flowing fluid. With the dome curved away from the pipe, the membrane would not prevent the flow from entering the pipe. But with enough pressure from the flow, the membrane would flip inside out and cover the end of the pipe, preventing fluid from entering.
Before building a valve, the team focused on the membrane alone in a fluid flow, without any other structures, by creating a mathematical model and by running computer simulations. While the model predicted the relationships between the various parameters in the system, the simulations provided a kind of digital “experiment”—direct numerical solutions of the fundamental equations for fluids and for elastic materials. The researchers also performed real experiments with membranes that were between 2 and 5 cm in diameter. Using silicone oil as the fluid, they varied the size, shape, and material of the membrane. The experimental data agreed with the theoretical predictions, for example, showing that the pressure when the flip occurs is proportional to the stiffness of the membrane. Finally, the team built a prototype valve and showed that it worked as expected.
Such a valve could be combined in a network with other valves and channels to direct flow along certain paths, the researchers say. They believe the valve could be used in soft robotics or wearable technology because the design uses a soft, flexible material and would be compatible with flexible pipes.
The team found “a simple yet robust design principle for passive flow switching,” says Ivan Christov, a mechanical engineer at Purdue University in Indiana. He also praises the new theoretical model, which he says could reduce the guesswork in microfluidics research. “Such basic soft-hydraulic principles are invaluable for designing microfluidic systems, as one needs to rapidly [develop] designs without running lengthy simulations or building many prototypes and testing them.”
–Elizabeth Fernandez
Elizabeth Fernandez is a freelance science writer based in Raleigh, North Carolina.
References
- P. G. Ledda et al., “Fluid-induced snap-through instability of spherical shells,” Phys. Rev. Lett. 135, 234002 (2025).