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Turn on the first pump, it pulls air and the pressure drops, through viscous flow and a bit into molecular flow, he pressure drop slows and then stops. The pump can't remove molecules any faster than they're leaking into the chamber. Turn on the second pump. It could probably viscous flow as it starts up, but as it's blades spin faster and faster (think jet engine) ....... then ion pump.......
Scroll pump standard model: Anest Iwata ISP-250C manual
Types of pumps
Roughing pump
operating pressures
scroll pump (animation of pumping action)
Turbomolecular pump (ie: turbopump, turbo)
operating pressures
turbopump blade action/molecule interactions:
Ion pump
operating pressures
Getter pump
Cryopump
https://uspas.fnal.gov/materials/15ODU/Session4_1_MechanicalPumps.pdf
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