Type DO is the most common form that uses an O-Ring as a secondary sealing element Type DO consist of two identical metal seal rings mounted in two separate housings face-to-face on a lapped seal face. The metal rings are centered within their housings by an elastomer element. One half of the Mechanical Face Seal remains static in the housing, while the other half rotates with its counter face. Product Applications Mechanical Face Seals are predominantly used for sealing the bearings in construction machinery or production plants operating under extremely arduous conditions and subject to severe wear. These include: Tracked vehicles, such as excavators and bulldozers Conveyor systems Heavy trucks Axles Tunnel boring machines Agriculture machines Mining machines Mechanical Face Seals are proven for use in gearboxes, mixers, stirrers, wind-driven power stations and other applications with similar conditions or where minimized maintenance levels are needed.