Fluid Leakage in Static Rubber Seals

Abstract

Interfacial surface roughness can result in fluid leakage of seals, and in the design of seals it is standard to give an upper limit for the surface root-mean-square (rms) roughness amplitude $$h_\text{rms}$$ h rms . However, $$h_\text{rms}$$ h rms is determined mainly by the long-wavelength roughness, which is (nearly) irrelevant for the sealing. I discuss the parameters which determine the leakage of seals, and present results for static rubber seals with circular cross-section (like rubber O-rings). I also study the influence of the fluid pressure on the interfacial surface separation and the leakrate. Graphical Abstract

Adhesion–Lubrication Paradox of Articular Cartilage

“…For typical materials, fluid flows easily within interfacial gaps between the rough surfaces, and the suction needed to drive the flow is small or undetectable. This situation is well illustrated by the lack of suction from the silicone control, which highlights how difficult it can be to seal an interface, even using very soft viscoelastic materials. , By contrast, the development of significant interfacial tension in the case of cartilage is itself evidence of effective interfacial sealing.…”

“…While interstitial (or poroelastic) suction is often described as a natural consequence of pull-off for biphasic materials, , it implies a sealed interface. Effective sealing is extremely challenging to accomplish due to the ease of fluid flow through gaps between the rough surfaces. , Cartilage is soft, but it is also rough on the scale of 1–10 μm . Thus, the fluid should prefer to flow through the micron-scale gaps between surfaces (paths of least resistance) rather than the nanoscale pores within the tissue. , The resulting interfacial suction force ( F s ) can be modeled as a squeeze film and depends on fluid viscosity (η), contact radius ( a ), retraction rate (δ̇), and mean gap height ( h ).…”

“…This fact appears to implicate suction as a more likely option. However, cartilage is rough, and rough surfaces promote interfacial flow, which disrupts suction. , The northern clingfish, which evolved to stick to rough and slippery underwater surfaces, resolved this problem using elastically independent hair-like microvilli that conform to rough surfaces, eliminate large interfacial gaps, and effectively seal the contact interface . How cartilage might achieve a similar function is an open question.…”

A novel finite element model for the flare joint contact status at the seal ring with multiscale factors during assembly

“…As a crucial component of the aviation hydraulic system pipeline, the sealing performance of ared pipe joints plays a vital role in the security and reliability of aircraft [4,5]. A ne contact status at the seal ring is required to prevent the pressure uid from leaking, whose formation is in uenced by multiscale factors during assembly [6,7].…”

On the use of surface roughness parameters

“…Thus assuming only elastic deformations the area of real contact depends mainly on the rms-slope ξ. Similarly, the leakage of seals is mainly dependent on ξ in contrast to the general assumption that the rmsroughness amplitude h rms is most important, and often used in design criteria [17]. The interfacial contact stiffness K depends mainly on the h rms , unless the applied pressure is so high as to result in nearly complete contact, or so low as to result in contact with just a few of the highest asperities.…”