How do rotary vane vacuum pumps that prevent oil backflow do so? It does not seem like they use check valves since check valves require a differential pressure drop to be effective and the rotary vacuum pumps are capable of pumping a vacuum below what a check valve will work with.
For example, the check valve on McMaster-Carr with the lowest operating pressure has it listed at 0.07psi which is 3600 microns. But these pumps can pull as low as a few tens of microns.
Nor does it seem like they use a solenoid activated valve.
