Oil Sample Bottle Types
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 aviation 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 above.
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 cleanliness 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 cleanliness levels. Fluids with greater cleanliness requirements, such as hydraulic fluid, demand cleaner sample bottles to help achieve an SNR value above 5.
Sample Collection
When a sample is taken, it is critical to know how much fluid should be drawn into the bottle. However, it may be more important to understand how much headspace or ullage is remaining in the bottle. This will help the laboratory perform proper agitation before testing. The amount of ullage required will depend on the fluid’s viscosity, as more viscous fluids need more room to agitate sufficiently.