Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/258778
42 | January - February 2014 | www.machinerylubrication.com Sample Bottle Material and Size Oil sample bottles are avail- able in a few standard materials, namely plastic or glass. The mate- rial should be selected based on the type of fluid sampled and the cleanliness requirements. The most common sample bottles are high-density polyethylene (HDPE) or polyethylene terephthalate (PET). HDPE is opaque, which may be its main disadvantage. Not having the ability to clearly see the oil in the bottle prevents visual onsite analysis, which can be helpful in detecting water or heavy particle contamination. On the other hand, PET is clear but generally not suitable for samples at temperatures higher than 200 degrees F. Nevertheless, it has greater compatibility with most industrial lubricants. Compared to glass bottles, both polyeth- ylene-based bottles are fairly inexpensive. However, glass bottles offer the benefits of excellent cleanliness levels and lubri- cant compatibility. The sample bottle size should be based on the type of sample fluid as well as the number and type of tests to be conducted. For most standard oil analysis tests, oil samples are taken in a 100- or 120-milliliter bottle. For advanced or exception tests, a 200-milliliter or larger bottle may be required, although bottles larger than 200 milliliters tend to be used for fuel analysis. An example of when a larger sample might be necessary would be for hydraulic fluid testing, especially avia- tion hydraulic fluid. Sample bottles can also come in smaller sizes for other applications. A breakdown of various types of oil sample bottles is shown in the chart on the left. When choosing an oil sample bottle, first talk to your oil analysis laboratory. Ask if the lab provides/recommends sample bottles. In addition, find out if the bottles are subjected to testing, as per ISO 3722. You then must establish the clean- liness requirements for your samples. One way to determine the necessary sample bottle cleanliness is to use the signal-to- noise ratio (SNR) technique. As the formula on page 45 indicates, the SNR is defined as the target cleanliness for the machine divided by the contamination identified for the bottle. The goal is a higher SNR value. For example, an SNR of 5 would have a 20-percent variance of cleanliness accuracy, while an SNR of 10 would have a 10-percent variance. A higher SNR is achievable with fluids like gear oil that don't require rigorous lessoNs IN lUBrICAtIoN USE VOLUME MATErIAL ISO CLEANLINESS* COST General oil sampling, visual analysis 3 and 4 ounces (100 to 120 milliliters) PET (transparent) Superclean $ General oil sampling 3 and 4 ounces (100 to 120 milliliters) HDPE (opaque) Clean to superclean $ Hydraulic fluid 4 and 8 ounces (100 to 200 milliliters) HDPE/PET (transparent or opaque) Clean to superclean $$ Hydraulic fluid, visual analysis 4 and 8 ounces (100 to 200 milliliters) Glass (transparent) Ultraclean $$$ * Cleanliness levels shown are of typical avail- ability and will depend on the bottle distributor. Oil Sample Bottle Types