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 ann ular grooves on one of the working faces. With the help of the back de pression grooves, a hydrostatic pressure and thereby a separating forc e with satisfactory stiffness are produced within the sealing gap. A m odel which takes surface roughness into account was used to predict th e performance of the seal. Relationships between the control parameter s (the recess position, r(G), the nominal film thickness, ho, the dept h, h(v), of depression grooves and the surface roughness parameter, a) are investigated against various pressure ratios, P-e/P-i. The analys is provides a simple optimum design procedure. A finite element analys is was carried out to account for the effect of face deformation durin g operation of the seal. Experiments for various speeds, pressures and roughness parameters were carried out and the results from the experi ments were used to validate the analysis performed. Analysis and exper iment revealed the importance of the surface roughness and deformation of the faces for the creation and retention of the gap.