Shop phrase for the first stage of a pump-down: opening the roughing valve so the mechanical or dry pump pulls the chamber from atmosphere to the crossover pressure. On manual systems it is a deliberate valve sequence (high vacuum valve shut, foreline valve shut, then roughing valve open), and getting the order wrong can dump a chamber full of air into a hot diffusion pump or a spinning turbo.
Rough it out to 100 millitorr, close the roughing valve, open the foreline, then crack the gate.
Also heard as
- rough down
- rough
- roughing
Related terms
Roughing pump
Pump that takes a chamber from atmosphere down to the pressure where the high vacuum pump can take over.
Crossover
Point in a pump-down where pumping switches from the roughing pump to the high vacuum pump.
Soft pump
Slow, throttled roughing from atmosphere that avoids stirring up particles and condensing moisture.
Pump down
To evacuate a chamber from atmosphere to its working pressure, through roughing, crossover and high vacuum.