Dry Gas Seals. Application of Double vs. Tandem Dry Gas Seal Advantages

Abstract

Tutorial 19B: Traditionally double seals have been used for low pressure applications when nitrogen gas at pressure higher than process was available for sealing. Double seals were not applied to low pressure processes where process contamination by nitrogen was not permitted. In these cases application of the process gas for sealing in a double seal was considered “unsafe” and the preference was given to a tandem seal. In recent years this approach has been re-evaluated and additional steps to insure safety in case of a secondary seal failure undertaken. Since both tandem and double seals can be used for applications with sealing pressure below approximately 40 bar, what benefits are to be gained by double seal application? Double seal arrangement, among other things, allows for system simplification and more reliable operation, significant reduction of sealing gas volumes, prevention of seal reverse pressurization and shorter in-between the bearings shaft span. A possibility of secondary seal failure and prevention of uncontrolled process gas emission can be addressed in a variety of ways - from incorporation of flow restriction to utilization of separation seal as safety seal.