Sensitivity analysis for the design and operation of a non-contacting mechanical face seal

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 eciently 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.

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].…”

Contact elimination in mechanical face seals using active control

“…In other cases, however, the load changes or the disturbances may vary substantially, causing large misalignment, beyond what rigid design can rectify. In the latter one or more of the operational variables, clearance, sealed fluid pressure, and shaft speed, can be used to actively control the seal behavior [6,7]. The analysis in [5] provides a solution for the dynamic response of the flexibly mounted rotor to two forcing functions: the fixed stator misalignment, and the initial rotor misalignment.…”

“…The maximum relative misalignment can be calculated according to the closed form solutions of the Green dynamic model [5,8]. Based on this solution, parametric and sensitivity studies [6,7,9] were performed to investigate the effect of basic seal parameters (including shaft speed, sealed fluid pressure, coning angle, and clearance) on the maximum relative misalignment for a noncontacting FMR seal test rig (shown in Fig. 2).…”

“…However, other factors, such as kinematics of the flexible support and its rotordynamic coefficients uncertainties, machine deterioration, transients in sealed pressure or shaft speed, or unexpected shaft vibration, affect the dynamic behavior of the seal and, hence, the relative position and misalignment between the rotor and the stator. The parametric studies ( [6,7,9]) explore the effects of various seal parameters on this γ max and provide valuable information concerning seal design and performance prediction. These studies also provide guidelines for contact elimination strategy.…”

“…The required control effort, i.e., the air pressure variations in the rotor chamber, seams to be very small. (6)(7)(8)(9)(10). Figure 6 depicts the changes in probe displacement signals obtained when the control is switched on and off.…”