Development Of A Twin Hybrid Noncontacting Gas Seal And Its Application To Process Pumps

Abstract

In this paper, an innovative approach of applying gas-lubricated, noncontacting sealing technology to process pumps is presented, in which a novel “twin hybrid” design is incorporated to address the issues of gas seal applications to process pumps. In this design, orifice-injected inert barrier gas between concentric twin seal faces gives rise to hydrostatic action, so that the inner seal face with hydrodynamic lift features upon running can initiate and maintain stable face separation, even at extremely slow speed. The outer plain face seal, by way of higher barrier gas pressure, prevents any process fluid on the outer diameter cavity from leaking or emitting through sealing faces. The twin face design compacting two seals to one seal ring not only reduces greatly the cartridge size so as to fit all pumps without stuffing box modifications, but maintains its dual seal functionality with the single seal simplicity. The hybrid feature combining hydrostatic action for start/stop and slow speed operations, and hydrodynamic action for initiating and maintaining stable face separation not only enhances the sealing performance, but also expands its application ranges. Detailed design features and operating principles including reducing O-ring hysteresis and pressure reversal or loss-of-barrier gas are discussed. Extensive laboratory and field test were conducted to validate the designs. A field test is described to exemplify its applications in process pumps including its performance in abnormal operating conditions.