The pump that evacuates a chamber from atmospheric pressure to crossover, usually a few tenths of a millibar, through a dedicated roughing line and valve. Rotary vane, scroll, dry screw and claw pumps fill the role, often with a Roots booster on large volumes. On small systems one pump both roughs the chamber and backs the high vacuum pump, switched between the two jobs by valves.
Roughing pump's struggling, it took twelve minutes to get the load lock to crossover instead of four.
Also heard as
- rougher
- rough pump
Do not mix it up with
- Backing pump: A roughing pump evacuates the chamber itself, while a backing pump holds down the exhaust side of a running high vacuum pump; one machine often does both jobs.
Related terms
Backing pump
Pump that keeps the exhaust of a turbo, diffusion or Roots pump below its maximum allowed pressure.
Rough out
To pump a vented chamber from atmosphere to crossover with the roughing pump, before the high vacuum valve opens.
Crossover
Point in a pump-down where pumping switches from the roughing pump to the high vacuum pump.
Rotary vane pump
Oil-sealed positive displacement pump in which sliding vanes sweep gas around an off-centre rotor.
Dry pump
Vacuum pump with no oil or liquid in its pumping chamber, used where oil vapour would contaminate the process.