 # How do I determine how much oil my CNG compressor is consuming?

Posted by on May 16, 2013 in Tips As a general rule of thumb, lubricant consumption at or above 50 brake horsepower (bhp) hours per once is considered an acceptable rate. To apply this principle, you have to know three basic things.

Motor Horsepower

Quantity of lubricant consumed. (see tip #2)

Number of operating hours.

For example: we are running an Ingersoll Rand Model 05H25NGSX, a simplex 25 horsepower compressor package. Through our log sheets we know that we have added 5 ounces of lubricant for every 20 hours of operation. The formula looks like this: 25bhp X 20 hours / 5 ozs = 100 bhp hours per ounce.

Some customers may require oil consumption reporting in parts per million (ppm). The conversion of oil consumption from bhp hrs/oz to ppm can be done if the capacity and horsepower of the compressor is known. The equation for the conversion of bhp hrs/oz to ppm for air is different than that of natural gas due to the differences in density between the two gasses.

For natural gas it is PPM = 202.61 X specific Power at test conditions (bhp per 100 scfm) divided by Oil Consumption (bhp X hrs divided by ozs) So, for the same IR package listed above we would calculate as follows:

PPM = 202.61 X (25 bhp / 28 scfm) / 25 bhp X 20 hrs / 5 oz = 180.90 ppm

The equation for converting ounces of oil to PPM is as follows: PPM = 20261 X (oz. oil/hrs) / scfm of gas at test conditions.

Email us with any questions you might have regarding oil consumption or the calculation of same.