Check the oil

What you find can indicate the health of your equipment. Using these tips as part of your proactive maintenance program will enhance your equipment's performance and boost productivity.

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By George B. Mullins

PlantServices.com

Lubricants are the lifeblood of industrial machinery. They protect critical components and help promote enhanced operation, just as blood supports health in the human body. And, while a doctor learns valuable information about a patient’s health through a blood test, you can garner valuable insights about your equipment using routine oil analyses.

Oil analysis is based on a slate of tests designed to help evaluate the condition of internal hardware as well as the in-service lubricant. With this information, you can extend the useful lives of both, by identifying early warning signs such as contamination or increasing wear metals which will allowing you to minimize unscheduled maintenance.

Below are some of the basics of oil analysis for the standard industrial applications: hydraulic systems, compressors and gearboxes. Using these tips as part of your proactive maintenance program will enhance your equipment's performance and boost productivity.

Take a representative sample

You must follow a certain protocol to ensure the accuracy and to gain the most benefit from your oil analysis results. First, always use a clean, dry container to draw oil samples. Store sample bottles in a clean dry, dust free area until the sample is taken.

Draw samples when equipment is at its normal operating temperature and while the machine is running, if it can be done safely. Otherwise, it is recommended to draw samples as soon as possible after the equipment has been shutdown.

A properly placed sampling valve complements an effective engineered analysis program. Ideally, take samples downstream of the filters, as it will most represent the condition of the oil that is supplying the critical lubrication points. To find the ideal sample point, review the equipment’s lubricating system. Normally, compressors and gearboxes are splash lubricated bath type reservoirs/sumps and hydraulic systems usually have circulation systems with a central reservoir housing the bulk of the oil.

The optimum sampling method for a circulation system uses a sampling valve or spigot at a high flow point just down stream of the filtration equipment.  If this point is not available, take samples from either the main return line or secondary points that are safely accessible.

When sampling through a fixed valve:

1. Remove the valve protective cap
2. Open the valve and drain about four ounces of oil through the valve into a slop bucket to flush any stagnant oil or contaminants that might have settled in the valve. Don’t close the valve.
3. Remove the sample bottle lid and avoid introducing any environmental atmospheric or surface contamination.
4. Collect your oil sample, filling the bottle only to the shoulder, leaving room for expansion and contraction.

If your analysis slate includes particle counts and you’re using standard production sample bottles instead of the “super-clean” variety, follow steps 4a through 4c to obtain the most representable sample.

4a. Dump the oil sample into the slop bucket to flush and remove any inherent bottle contaminants. Don’t close the valve.
4b. Collect another oil sample and discard it, too.
4c. Collect your final oil sample, filling the bottle only to the shoulder.
5. Replace the sample bottle lid.
6. Close the sampling valve.
7. Replace the protective cap on the valve.
8. Fill out the sample label and attach it to the bottle.
9. Record any unusual operating conditions (noise, leaks, temperature, vibration, etc.).

Avoid sampling from reservoirs where possible as stratification and sediment can produce unrepresentative samples that will adversely skew the results. If the equipment doesn’t have a circulating system, which is the case for some gearboxes, take samples from the gearbox bath or sump. Insure that samples are taken several inches from the bottom of the bath, to avoid accidentally including the insolubles/sludge layer that has appropriately settled to the bottom.

If you have any question about the most appropriate sample point, consult the machine manufacturer for advice. Once the optimum sampling location has been identified, note it in the maintenance records. This ensures that future test results will provide the most accurate trend line and level of insight.

Viscosity can be a variable

Viscosity is a measurement of a lubricant’s resistance to flow. This variable or characteristic is the most critical parameter for most applications and can change over time or more quickly in equipment that sees extreme temperatures or high pressures or high speeds. Always monitor lubricant viscosity closely, to ensure that it is within the targeted viscosity range which will minimize wear between critical equipment components. Some typical ISO viscosity grades for various industrial applications include:

• Hydraulic systems: typically around ISO-46 to 68 but can range from ISO 32 to 220 based on service type where temperature, speed or load demands can vary.
• Gearbox: typically around ISO-220 to 320 but can range from ISO 150 to 1000 based on service type where temperature, speed and load demands can vary.
• Air compressors: most typical is ISO-46/68 but can range from ISO 32 to 150 based on temperature, speed and load demands can vary.

If the viscosity changes by +/-15% of its original value, monitor the oil more frequently. Equipment can perform normally if the lube is outside of this range, but it should be watched more closely as this usually indicates changes are needed. All equipment applications have stated recommended operating temperatures and recommended lubricants that meet that condition.  If oil temperatures significantly vary (particularly trending higher) it is recommended to re-review the ISO grade of the oil to ensure that an appropriate film thickness is being provided to insure efficient wear-free performance.