We would prefer to mist the bearing oil by pushing it through an injector, but to mist 30 weight oil takes between 5000 and 7000 psi (340 to 475 bar) and that pressure is not available on process pumps.

If you pump an air oil mist into a bearing case there is going to have to be a vent somewhere to prevent a pressure build up.

It is this oil mist venting that presents possible fugitive emission problems.