Excessive concentrations of water vapor present in vacuum pumps make the lubrication of these machines a difficult task. Vacuum pumps require very specific types of lubricants that may withstand the environmental conditions and extreme temperatures that these machines operate in.
ISO VG 46 oil has a midpoint kinematic viscosity of 46 mm2/s, also referred to as centistokes (cSt). The midpoint is derived by taking the average of both the minimum and maximum kinematic viscosities. In the case of ISO VG 46 oil, those numbers are 50.6 cSt and 41.4 cSt, respectively. These numbers refer to the standard testing mechanisms used to determine how much resistance to flow (i.e. viscosity) these oils demonstrate.