To take a chamber from atmosphere to operating pressure; as a noun, a pump-down is the whole sequence of roughing to crossover, opening the high vacuum valve and pumping to base or process pressure. In the rough range the time follows t = (V/S)·ln(p0/p), set by volume and pump speed, while in high vacuum outgassing takes over, so a clean, dry chamber pumps down in minutes and a wet one takes hours.
Pumped down at seven and we're at 5E-6 already, the door seal must have been the problem.
Log the time to crossover and to a reference pressure on every cycle; a slow upward drift flags a wet chamber or a tiring pump before base pressure does.
Also heard as
- pump-down
- pumpdown
- evacuate
Related terms
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.
Pump-down curve
Plot of chamber pressure against time during a pump-down, used as the fingerprint of a healthy system.
Vent
To let gas back into an evacuated chamber, usually dry nitrogen, to bring it up to atmosphere.
Base pressure
The lowest pressure a particular chamber reaches after pumping for a set time with no process gas flowing.