Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/325287
46 | May - June 2014 | www.machinerylubrication.com sampling valve option is a minimess valve, which ensures no disturbance to the machine's operations. If the wet sump is configured with a kidney-loop filtration system, a similar sampling location can be selected. For this config- uration, a minimess valve for sampling can be installed after the pump and before the filter in the same manner that the supply-line system was equipped, since the system is also in a pressurized state. Many filter housings have convenient ports just upstream of the filter, which are often used for pressure gauges. Non-Circulating System In systems without any circulation of lubricating oil, the primary means for obtaining a sample will be through the system's sump casing using a pilot tube from the sample valve to draw fluid from a turbulent, live-zone location. These types of systems will have a drain plug either near or at the bottom of the sump. This is where the sample port can be installed along with a T-adapter to allow for the addition of a ball valve for draining. Minimess valves can be installed at an oil level port where a sight glass is typically situated. If this port is the most accessible, then a device that enables both sampling and sight glass functionality will be necessary. During installation, the pilot tube should be carefully positioned so the tip is in an ideal live-zone location. Generally, this will be halfway up the oil level and a sufficient distance from any walls. It must be close to turbulent areas but no closer than two inches from any moving elements or walls within the system. The best hardware to use in conjunction with the minimess sample port would be a vacuum sampler. This helps ensure that the sample never comes in contact with the environment. Sampling Frequency How often should sampling be performed? This is not a simple question. Basically, it is a tradeoff. Sampling less frequently can risk missing a machine or lubricant failure, while sampling more frequently can risk wasting time and money (and even lubricant). A better question would be, "What are the variables that help calcu- late the optimum sampling frequency?" These variables would include the machine age, oil age, target tightness, fluid environment severity and economic penalty of failure. For a description of each variable, see the sidebar on this page. All of these variables are best determined by the individuals who are most familiar with the machine being sampled. Many of these questions asked about the machine are subjective, and the most effective way to develop appropriate answers is to use historical information related to past machine failures, machine criticality, lubricant type, failure modes, lubricant change-outs and top-ups, adjustments to oil analysis targets over time, fluctuations in envi- ronmental conditions, etc. Simply stated, the more you know about the machine, the better you will be able to calculate the optimum sampling frequency in rela- tion to the key variables. Often you need to make intelligent adjustments to machine sampling frequency to optimize the value gained from oil analysis. This subject is discussed more extensively in Jim Fitch's column on Unified Condition Monitoring (on page 2). About the Author Bennett Fitch is a technical consultant with Noria Corporation. He is a mechanical engineer who holds a Machine Lubricant Analyst (MLA) Level III certification and a Machine Lubrication Technician (MLT) Level II certification through the International Council for Machinery Lubrication (ICML). Contact Bennett at bfitch@noria.com. lessoNs IN lUBrICAtIoN 1. Economic Penalty of Failure – Sampling should be taken more frequently when the cost of downtime, repair, rebuild, interruption to business and/or impact of product quality are high. 2. Fluid Environmental Severity – Sampling should be taken more frequently when demands placed on the lubricant by the environment and/or the machine are high. 3. Machine Age – Based on the "bathtub curve," sampling should be taken more frequently when the machine is young (infant mortality) or old (surpassed maximum useful life). 4. Oil Age – Same as machine age, during the life of a lubricant in a machine, samples should be taken more frequently when the age of the oil is new or old. 5. Target Tightness – Sampling should be taken more frequently when oil analysis targets (such as ISO particle counts) are approaching or consistently near the goal-based limits. 5 variables for Calculating Sampling Frequency