Air, helium and water leakage in rubber O-ring seals with application to syringes

TL;DR

This paper investigates fluid leakage in syringe O-rings, highlighting how surface roughness and rubber properties influence leak rates for gases and liquids, with a simple theory explaining ballistic gas flow.

Contribution

It introduces a simple theory for gas leakage considering ballistic flow and compares leak rates of air, helium, and water in syringe seals.

Findings

Gas leakage is mainly ballistic due to narrow channels.

Leak rates differ significantly between gases and liquids.

Capillary effects prevent water leakage despite gas leakage.

Abstract

We study the leakage of fluids (liquids or gases) in syringes with glass barrel, steel plunger and rubber O-ring stopper. The leakrate depends on the interfacial surface roughness and on the viscoelastic properties of the rubber. Random surface roughness is produced by sandblasting the rubber O-rings. We present a very simple theory for gas flow which takes into account both the diffusive and ballistic flow. The theory shows that the interfacial fluid flow (leakage) channels are so narrow that the gas flow is mainly ballistic (the so called Knudsen limit). We compare the leakrate obtained using air and helium. For barrels filled with water we observe no leakage even if leakage occurs for gases. We interpret this as resulting from capillary (Laplace pressure or surface energy) effects.