Back to Basics - Rubbing or Not? Part 2

Back to Basics: Fluid Induced Instability; i.e. Oil Whirl / Oil Whip

Metrix SETPOINT Contition Monitoring Group; Minden, NV

When a fluid, either liquid or gas, is constrained within the space between two concentric cylinders, one rotating and one stationary, the fluid in the clearance between the two cylinders will be set into circumferential motion. This can happen in rotating machinery within the fluid-lubricated bearings, seals, around pump impellers, or in any fluid filled gap between the rotor and the stator. 

Hot spot analysis helps reduce spiral vibration of a hydrogen-cooled generator

An Alstom 450MVA hydrogen-cooled generator operating at 3,600 rev/min and equipped with a brush gear unit showed spiral vibration with a forward rotating unbalance vector. 

Back to Basics - Rubbing or Not?

Metrix SETPOINT Contition Monitoring Group; Minden, NV


The first item to be realized is that radial or axial rubbing is not a machinery malfunction.  A rub is secondary indicator that occurs when there is contact between rotating and non-rotating components.  Some of the primary causes that can lead to a rub are:

Rubs and Their Vibration Behavior

Richard Thomas

Richard Thomas has over 38 years of rotating equipment experience in industry and currently holds the position of Prinipal Engineer for Metrix Instrument Company. Prior to his current position, his work experience included 11 years as a rotating equipment engineer in the petrochemical industry; 17 years in the Engineering Services Department of Bently Nevada Corporation; and 6 years as the Global Services Manager for RoMaDyn Corporation.

Second Order Kalman Filter for Vibration Monitoring


Should I Install Single Plane or XY Proximity Probes?

Richard Thomas, P.E.

Dissipating Rotor Vibration Energy via a Fluid Film Bearing

Richard Thomas, P.E.

The following statement is often referred to as the “1st Law of Machinery Diagnostics”:

Vibration Displacement (Vector Quantity) =

Summation of Forces Acting on the Rotor System (Vector Quantity) divided by the System Dynamic Stiffness (Vector Quantity)

Shaft Average Centerline and DC Data Plots

Most vibration data plots, including: Timebase, Orbit, Polar, and Bode, present dynamic vibration data.  For seismic transducers, this dynamic data is inertially referenced to ground.  For the case of the shaft relative proximity probe, the dynamic vibration occurs about a –dc gap voltage, with the –dc gap voltage being proportional to the average distance from the probe tip to the target (shaft).  These data plots display dynamic vibration data, but do not show changes in the average shaft radial position, an important response characteristic of the rotor syste


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