How a leak can stop itself

Small fluid leaks are common and frequently troublesome. We often consider how to stop a leak, but here we ask a different question: how might a leak stop itself? We experimentally study leaking flow transitions from continuous drainage to spontaneous arrest. High-speed imaging reveals that fluid breakup events generate droplets whose Laplace pressures oppose the leak. Early droplets grow unstably, allowing the leak to continue, but ultimately a final capping droplet equilibrates to a stable spherical cap via lightly damped harmonic oscillations. A total energetic theory incorporating both the potential and kinetic energy of attempted capping droplets shows that inertia plays a key role in the leak-stop mechanism. Further experiments examining the stability of rivulet flow in such a system demonstrate that a transition from continuous to discrete flow is an essential prerequisite in determining when a leak can stop itself.