Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/468007
www.machinerylubrication.com | January - February 2015 | 35 Stay Connected With Noria Follow us on Twitter https://twitter.com/NoriaCorp Like us on Facebook http://www.facebook.com/noriacorp Connect with us on LinkedIn https://www.linkedin.com/company /noria-corporation Continue learning with us on YouTube http://www.youtube.com/user/noriacorp both viscosity values. A common term used in conjunction with density is specifi c gravity, which is the relationship of density to water. Water has a specifi c gravity of one, so if a fl uid is heavier than water, the specifi c gravity value will be more than one. Anything lighter than water will have a value that is less than one. This property of a fl uid is crucial for several attributes of a lubricant. For instance, as the density of a lubricant increases, the fl uid becomes thicker. This leads to an increase in the amount of time it takes for particles to settle out of suspension. The specifi c gravity of rust falls somewhere between 2.44 to 3.6, so as the oil thickens, particles such as this settle out much slower in reser- voirs and other areas with dwell time in the fl uid. In hydraulic systems, this can cause failure. These types of systems are very sensitive to any contamination. Therefore, if the particles are in suspension longer, it can result in problems such as silt lock, cavitation and corrosion. In E.C. Fitch's Proactive Maintenance for Mechanical Systems, many other problems associated with density deviations are given, particularly in hydraulic systems. These include a greater propensity for cavitation (both at pump suction and downstream of orifi ces), decreased pumping power, increased stress on pumping elements and poor pumpability due to fl uid inertia. According to Fitch, "High-density fl uid contributes to better contamination control by aiding in the suspension, transport and removal of particulate contaminants." Since the particles are held in suspension longer, they are more easily removed by fi lters and other particle- removal systems, thus making it easier to clean the system. It is important to note that some fl uids used as lubricants are in fact heavier than water. Most phosphate-ester fl uids have a specifi c gravity of more than one. In these systems, water would fl oat on top of the oil. Keep in mind that as density increases, so too does the erosive poten- tial of the fl uid. In high turbulence or high-velocity regions of a system, the fl uid can begin to erode piping, valves or any other surface in its path. Not only are solid particles affected by the density of a fl uid, but so are contaminants such as air and water. Both of these contaminants have a marked impact on density. Oxidation infl uences the density of a fl uid as well. As oxidation progresses, the density of the oil increases. Overall, density plays a critical role in how a lubricant functions and how machines perform. Most systems are designed to pump a fl uid of a specifi c density, so as the density begins to change, the effi ciency of the pump begins to change as well. Understanding the importance of density and how it relates to your equipment is essential for the reli- ability and health of your machines. If you have a question for one of Noria's experts, email it to editor@noria.com.