Seal clearance control is an advancement in noncontacting mechanical face seal operation because seal clearance variation caused by process disturbances may cause either severe face contact or excessive leakage, each of which is regarded as seal failure. The objective of this research is to control the seal clearance at a desired value overcoming operation disturbances, including variations in shaft speed and sealed fluid pressure. A flexibly mounted rotor (FMR) noncontacting mechanical face seal test rig is used in this study. The clearance control concept is to adjust the closing force that acts upon the flexibly mounted rotor. The seal clearance is measured by an eddy current proximity probe. The seal axial dynamic model is experimentally determined for the design of a proportional-integral (PI) controller with anti-windup. The controller is then applied to the test seal. Results show that the controlled seal maintains or follows set-point clearance changes with and without disturbances in sealed water pressure and shaft speed. The controlled seal is shown to respond quickly (having a small time constant) with a small control effort.Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 26–28, 1998