Ph.D. Thesis Defense by Min Zou
Friday, December 4, 1998

(Dr. Itzhak Green, advisor)

"Real-Time Monitoring and Control of a Noncontacting Mechanical Face Seal "

Abstract

Mechanical face seals are the most versatile type of rotating shaft seal. Despite their wide applications in industry, mechanical face seals generally have unpredictable life and their premature and random failures are very common. Seal failures are often characterized by worn faces caused by rubbing contact between seal faces even in noncontacting operations. The objective of this research is to develop a system for real-time monitoring, contact detecting, and control of a noncontacting flexible mounted rotor (FMR) mechanical face seal test rig.

Parametric analysis is performed to understand the effect of seal geometry and operational parameters on seal angular response. Dynamic simulation is also carried out to investigate the seal rotor angular response to the stator misalignment, the stator angle, the initial rotor misalignment, and the seal clearance. Rotor angular response orbit is introduced and found capable of characterizing the rotor dynamic response. A real-time monitoring system for the test seal is then established. Eddy current proximity probes are used to measure the rotor response. Algorithms are derived and coded to calculate important rotor response parameters, such as rotor angular misalignment and precession, relative misalignment between the rotor and the stator, and the seal clearance.

Seal face contact is detected by analyzing the signals obtained by the proximity probes. Either spectrum analysis, or the rotor angular misalignment orbit is used. One indication of contact is the presence of higher harmonics oscillations, which are integer multiples of the rotating shaft speed. The shape of the orbit can also indicate the presence of face contact.

Both clearance control and contact control are implemented in the test rig. The control system adjusts the closing force that acts upon the flexibly mounted rotor. Under clearance control, the seal can maintain a certain clearance or follow clearance set-point changes even when disturbances in sealed water pressure and shaft speed exist. The contact controller takes action to reduce the rotor angular misalignment and, therefore, to eliminate face contact once it is detected.