Contact elimination in mechanical face seals using active control

Abstract

Wear and failure of mechanical seals may be critical in certain applications and should be avoided. Large relative misalignment between the seal faces is the most likely cause for intermittent contact and the increased friction that eventually brings failure. Adjustment of the seal clearance is probably the most readily implemented method of reducing the relative misalignment and eliminating seal face contact during operation. This method is demonstrated with the aid of a noncontacting flexibly mounted rotor (FMR) mechanical face seal test rig employing a cascade control scheme. Eddy current proximity probes measure the seal clearance directly. The inner loop controls the clearance, maintaining a desired gap by adjusting the air pressure in the rotor chamber of the seal. When contact is detected the outer loop adjusts the clearance set point according to variance differences in the probes' signals. These differences in variance have been found to be a reliable quantitative indication for such contacts. They are complimentary to other more qualitative phenomenological indications, and provide the controlled variable data for the outer loop. Experiments are conducted to test and verify this active control scheme and strategy. Analysis and results both show that contrary to intuition for the seal under investigation, reducing seal clearance can eliminate contact, and the outer cascade loop indeed drives the control toward this solution.

Crack Detection in a Rotor Dynamic System by Vibration Monitoring—Part II: Extended Analysis and Experimental Results

“…The seal face contact detection system diagnoses contact based on relative variance between the proximity probe signals [21,[26][27][28]. However, the total tilt orbit shape Experimental totai tilt orbits near respective 2X resonance locations for cracks between 0% and 30% depth for the sealing system when contact is occurring is mostly circular [28].…”

“…The ability of the test rig to detect higher harmonics due to seal face contact is discussed in Ref. [20], and an active control system is proposed by Dayan, Zou, and Green [21] to eliminate the contact. Modifications to the test rig allowing shaft crack detection, as first proposed in Part I, are provided herein with the goal of discussing the feasibility of simultaneous multiple-fault detection.…”

Dynamic simulation and monitoring of a non-contacting flexibly mounted rotor mechanical face seal

“…A control system that can take meaningful action based on the real-time dynamic monitoring and contact detection results is currently being incorporated [12,13]. …”

“…A more advanced and proactive step in face seal dynamics is to control the seal rotor dynamic behaviour and prolong its life. A control system that can take meaningful action based on the real-time dynamic monitoring and contact detection results is currently being incorporated [12,13].…”

Impact Phenomena in a Noncontacting Mechanical Face Seal

“…Most previous studies focus on detecting contact experimentally using methods such as vibration monitoring [15,16,18], ultrasonic techniques [19][20][21], acoustic emission [22,23] or a combination of methods [24]. Others have used these same experimental measurement techniques to heuristically identify contact signatures and apply these signatures to an activelycontrolled seal in an attempt to eliminate contact [25][26][27][28].…”