Normalizing Data For Makeup Oil
Adding makeup oil between oil samples affects the data because of dilution
Fortunately, we can apply a simple formula based upon the amount of makeup oil added to adjust the values for dilution between samples. Here's the proper steps involved:
- Determine normal full sump capacity
- Determine amount of oil added since last oil change
- Sample after makeup at normal full sump capacity
- Convert wear metal and contaminant values to normalized values
In this hypothetical example, let's assume you have a 12 quart sump capacity and have added 3 quarts of makeup oil since your last oil change and oil sample.
To convert, multiply your measured values by the normalized value you have calculated (in this case: 1.25ppm)
Note: normalized values are crude estimations. These are based on the assumption that all of the "made-up" oil leaked out at one time and no wear debris left the sump with it.
Normalizing the values for oil additives involves a slightly different concept and uses a more complicated formula. The formula for normalizing makeup oil for additives is:
- A = Measured concentration
- B= Volume of makeup oil added
- C = Normal sump volume
- D = New oil additive concentration
Grant Dawson - Laboratory Data Analyst, OMA I, MLA I, MLA II
www.oilanalysis101.com
www.analystsinc.com
Do you have a formula that can be applied to large turbine oil sumps. Additives and wear metals are minimal in those samples, but there are several other concern. Probably too much going on in those sumps to be considered, but sweetening is a common practice with varying results.
That is correct: most samples do not arrive with this info. The ones that do provide such info usually involve components with critical applications.
The lab does not usually get oil top off information from the customer when samples are submitted for testing - and we do not usually have sump capacity data either
In the world of natural gas compression systems, this is called 'oil sweetening'. The engine sump is bled off to feed the compressor cylinder lube system, thereby continuously diluting the engine oil. The benefits are twofold: 1) dramatically delay the need to change the engine oil, and 2) comply with EPA's RICE NESHAP rules by keeping the TBN levels away from the min. thresholds which would dictate an oil change.