These vacuum coseals for NW/KF20-25 flange fittings are made of a polymer-supported Viton O-ring.Coseals represent a major advance in the method of sealing NW and ISO flange connections. The seal design eliminates crevices and trapped gas volumes (there is nothing between the Viton vacuum seal and the gas media). When properly fitted, the inner face of the Coseal is directly exposed to the vacuum system, eliminating any crevices or trapped volumes, which can generate gas bursts and inhibit pump-down.
Unlike the regular centering ring and O-ring, the NW Coseal is fully restrained externally. Coseals are available with either nitrile or fluoroelastomer (Viton) seals.