The Type 211 pair of packing rings consist of two tangent to the step rings pinned together to overlap at the step. This design has traditionally been used to seal low pressure or vacuum applications. The pair of tangent rings allows the 211 style to seal in both directions. Because of the large sealing surface, more frictional heat is generated and therefore greater wear to the piston rod and the seal itself. The 211 design does not allow gas to pass back through the packing case when pressure drops from discharge to suction in the cylinder, therefore its application should be limited to low pressures such as after the vent connection, vacuum service or in partition packings.
