To let gas in deliberately and slowly, through a needle valve, a variable leak valve or a mass flow controller. Techs bleed nitrogen into a foreline to keep a rotary pump in viscous flow so it cannot backstream, bleed argon into a chamber to set sputter pressure, or bleed a known gas in to calibrate an RGA. A bleed is also the small gas line or valve used to do it.
Bleed a little nitrogen into the foreline when the system idles overnight so the mech pump doesn't backstream.
Also heard as
- bleed in
- leak in
- bleed valve
Related terms
Backstream
Of pump oil or vapour, to flow the wrong way, from the pump back toward the chamber.
Backfill
To fill an evacuated chamber with a chosen gas, often to a set pressure, rather than with room air.
RGA
Residual gas analyzer: a small mass spectrometer that identifies which gases remain in a vacuum chamber.
sccm
Standard cubic centimetres per minute: a mass flow unit for process gases, referred to 0 °C and 1 atm.
Same word, different worlds
Separation of oil from a grease, either as a storage problem or as the intended release of oil to a bearing.
Boilers & BurnersTo let trapped air out of a hot water radiator, baseboard or high point by opening its small vent until water appears.
Sealants & WaterproofingStaining from fluids or plasticizers that migrate out of a sealant into porous stone or masonry.