Static sealing

The very good static sealing for the Metseal seal is based on three fundamentally important factors. The first and most determining factor is that the Metseal piston ring of metal is slender and can follow the cylinder bore and maintain full contact around the whole circumference. The only practical flow path for a possible leakage is inside the profile of the area of contact between the cylinder bore and the seal. Such a flow could take place inside the surface profile in between grooves and crests and give laminar flow. We are talking about flow paths with a dimension of less than 1 micrometer (μm) between the walls. The volume of such a flow is proportional to the wall distance, elevated to 3 or 4. One can compare with formulas for flows in plain parallel gaps or circular bores. With the minute dimensions between the walls involved, the potential flow will be so low that clogging phenomena will prevent it occurring. The second determining factor that entirely prevents flow within the surface structure, is the phenomenon that ensures that the surfaces will be covered by a semisubstantial boundary layer. This same boundary layer provides lubrication at the highly loaded points of contact in ball and roller bearings and between the teeth of toothed gear drives. The presence of this thin boundary layer in the surface grooves between the Metseal and the cylinder bore ensures that absolute sealing takes place. In addition to the solid boundary layer, long oil molecules are trapped at scratches, craters and other relatively big surface imperfections to contribute to the oil tightness of the seal. Oil tightness can thus be achieved even with poor and damaged surfaces. The third determining factor for the highest possible oil tightness is that the Metseal seal, like the cylinder bore has hard and rigid surfaces. The seal and bore make contact only at their surface crests. Freedom from elasticity ensures that the contact area remains stable. The sealing layer located in the valleys is therefore undisturbed by the sliding movements of the seal inside the bore. From the point of view of flowing, the seal and cylinder are operating with entirely flat surfaces and no open flow. Example of this function is a high-pressure gas spring (300 bar) which become entirely static tight with the aid of a few drops of oil. In a seal made from polymeric material the sealing surface will distort and the seal will move elastically into the surfaces valleys. This movement will inhibit and prevent the formation of the desirable thick semi-solid boundary layers.