Basic principle of unit conversion of oil content
the oil content in compressed air is usually in mass concentration (mg/ m³) or volume concentration (ppm, that is, μl/L). The conversion between the two needs to be based on the density and molar mass of oil vapor, but in practical application, the industry generally adopts approximate conversion relationship: 1 mg/ m³ ≈ 0.08-0.12 ppm (depending on oil type, temperature and pressure conditions). For typical mineral oil (average molecular weight about 200g/mol, density about 0. 85 g /Cm³), in the standard state (0 °C，101.325 kPa), 1 mg/ m³ about corresponding0.095 ppm.
ISO 8573 provisions in the standard
ISO 8571-1:2010 the compressed air quality is divided into different grades, in which the oil content is evaluated uniformly in the form of total oil (liquid oil, oil mist and oil vapor), in mg/ m³. This standard does not force ppm expression, because ppm is susceptible to temperature and pressure, while mg/ m³ more comparability and Measurement stability. When conversion is required, reference conditions (such 20 °C, 101.3 kPa) and explain the oil density used.
Oil Mist concentration and measurement method
- oil Mist (suspended liquid oil droplets) is one of the main oil forms in compressed air, which is usually measured by condensation method or laser scattering method;
- the total oil content includes oil mist, oil vapor and condensate. ISO 8573-2 and ISO 857-5 joint detection of prescribed methods;
- pure mg/ m³ conversion to ppm is not applicable to oil mist-because it is non-gaseous, ppm is only strictly applicable to gaseous components.