Performance study of a back-depression mechanical dry gas seal

An aerostatic mechanical dry gas seal is described in this paper. The seal has shallow depression grooves (compensators) on the back and annular grooves on one of the working faces. With the help of the back depression grooves, a hydrostatic pressure and thereby a separating force with satisfactory stiffness are produced within the sealing gap. A model which takes surface roughness into account was used to predict the performance of the seal. Relationships between the control parameters (the recess position, rG, the nominal film thickness, h0, the depth, hv, of depression grooves and the surface roughness parameter, a) are investigated against various pressure ratios, pe/ pi. The analysis provides a simple optimum design procedure. A finite element analysis was carried out to account for the effect of face deformation during operation of the seal. Experiments for various speeds, pressures and roughness parameters were carried out and the results from the experiments were used to validate the analysis performed. Analysis and experiment revealed the importance of the surface roughness and deformation of the faces for the creation and retention of the gap.