The line between the outlet of a turbo, diffusion or Roots pump and the backing pump, together with any valve, trap or gauge on it. Its pressure, read by a Pirani or convection gauge, is the health signal for the whole stack because it has to stay below the high vacuum pump's critical backing pressure. Foreline traps, filled with molecular sieve or kept cold, stop oil from the backing pump creeping up toward the high vacuum side.
Foreline's sitting at 0.5 torr with no process gas, something's leaking between the turbo and the dry pump.
Also heard as
- fore
- backing line
Related terms
Backing pump
Pump that keeps the exhaust of a turbo, diffusion or Roots pump below its maximum allowed pressure.
Pirani gauge
Thermal conductivity gauge that reads pressure from how quickly gas carries heat away from a hot wire.
Backstream
Of pump oil or vapour, to flow the wrong way, from the pump back toward the chamber.
At speed
Said of a turbo pump that has finished spinning up and reached its normal rotational speed.