Sensitivity analysis for the design and operation of a non-contacting mechanical face seal J Dayan, M Zou and I Green* The George W. Woodru School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA Abstract: Detection and diagnosis of failure in non-contacting mechanical face seals may prevent catastrophes in some critical applications. Seal failure due to face contact may occur because of large relative misalignment between the seal rotor and stator faces. The objective of this work is to study the sensitivity of the relative misalignment to changes in the design and operational parameters of a non-contacting ¯exibly mounted rotor (FMR) mechanical face seal. These sensitivities can be e- ciently exploited to prevent possible contact through proper selection of the seal parameters and working point in both the design and the control stages. Among the design parameters, the seal coning angle is by and large independent of other design requirements and should be properly selected to avoid contact. The operational variables greatly in¯uencing the relative misalignment are the clearance, the bearing ¯uid pressure and the shaft speed. Where active control is considered, the relative misalignment sensitivity to changes in the control parameters should determine the working point. The sensitivity analysis is demonstrated using the data of an existing seal test rig. Keywords: non-contacting mechanical face seal, sensitivity, parameter analysis, control NOTATION A matrix de®ned in equation (9) C matrix de®ned in equation (9) C o maintained clearance D  damping coecient F set of governing equations [equation (7)] I  , I  z rotor transverse and polar moments of inertia K  stiness coecient m  rotor mass P  ¯uid pressure r  radial coordinate R dimensionless radial coordinate  r=r o s sensitivity vector [equation (5)] ~ s non-normalized sensitivity vector (Table 3) S seal parameter  6!r o =C o  2 1  R i  2 S elementary sensitivity matrix [equation (6)] x dimensional input vector [equation (3)] y dimensionless dependent vector [equation (2)]   face coning angle   misalignment P io pressure drop across the liquid ®lm  viscosity ! shaft rotating speed Subscripts cr critical f ¯uid ®lm i inner radius m mean o outer radius r rotor ri initial rotor misalignment rI rotor response to initial misalignment s support 33 axial Superscripts * dimensional, non-normalized variable De®nitions D 33  D s33  D f33 total axial damping coecient D f33  4pR m G o ®lm axial damping coecient D  s  1 2 D  s33 r 2 s dimensional support angular damping coecient The MS was received on 25 February 1999 and was accepted after revision for publication on 5 July 1999. *Corresponding author: The GWW School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405, USA. 1207 C03799 ß IMechE 2000 Proc Instn Mech Engrs Vol 214 Part C