Viscosity Analysis: Oil Condition Monitoring
Posted on Wed, Sep 07, 2011
Viscosity Analysis: Oil Condition Monitoring
Ever notice that engine failures always seem to occur far away from a repair 
facility? Such breakdowns are frequently due to bearing failures on rotating parts, a condition that can readily be prevented by monitoring the viscosity of the lubricating oil.
“Viscosity breakdown can be due to fuel dilution, additive oxidation, soot, water and other contaminants or thermal degradation,” says the vice president of engineering for a company providing maintenance for locomotives in the U.S. “We need to know when the lubricant oil condition is changing to minimize the impact of failure. Unfortunately, all too often, lubricant viscosity deteriorates and bearings are damaged between laboratory oil analyses.”
Concerned about this, he instrumented a locomotive that had been designated as high risk with an on-board viscometer mounted in its lubricating oil recirculating line. The locomotive was then placed back in normal service. For a long time, the viscosity tracked as designed with a viscosity of 15-15.5 cP, and was verified at the occasional laboratory stops. Then, the on-board instrument showed the viscosity dropping.
As the oil viscosity dropped from normal to marginal (about 13 cP) over a period of 15 hrs and 40 minutes, the engineer hoped he would be able to reach the next repair facility. Throughout the next eight hours, the viscosity dropped through the warning condition (12 cP), toward critical (11cP). It arrived at the repair facility just in time. The locomotive was changed out so that the train could continue on its schedule. The engine problem was verified, and overhauled, with significant savings for the company.
To identify on-engine viscosity breakdown, the locomotive maintenance company utilized a Cambridge Viscosity VISCOpro1600/571 viscometer, which is small, accurate and robust. Further, it incorporates temperature compensation to adjust for normal temperature effects on viscosity readings. The Cambridge sensor was mounted on a by-pass line, which diverted a small volume of oil from the engine into a thermally-controlled chamber. There, the sensor operates with a magnetically-driven piston oscillating inside the sample chamber, and the oil’s resistance to flow is a direct measure of the time it takes the piston to travel across the chamber.
“CVI’s VP1600/571 is ideal for oil condition monitoring,” says Cambridge President Robert Kasameyer. “It answers all the rigorous demands of high quality onsite lubricant analysis, and with its miniature footprint, it offers the smallest in-line sensor available. It detects small changes in viscosity in real-time such as a .25% fuel dilution, and is insensitive to flow and vibration for highly reliable information.”
About Cambridge Viscosity
Cambridge Viscosity, the leader in small sample viscosity systems, provides automated viscometers used for oil analysis and condition monitoring as well as in oil exploration, refining, coating, chemical and life science companies to optimize product and process performance. Cambridge's global reach provides application engineering support and service wherever and whenever needed.