A leak, typically above about 10⁻⁴ mbar·L/s, large enough that the chamber stalls in the rough range, the roughing pump gurgles, or a bubble test can see it. Gross leaks are hunted by listening for hiss, with bubble solution on pressurized parts, or by dabbing alcohol on joints and watching a Pirani jump, before fine leak methods come out. A helium detector that meets a gross leak can be overwhelmed and left with long hang-up.
Chamber stalls at 3 torr, that's a gross leak, check the door O-ring before you drag the helium cart over.
Also heard as
- big leak
- coarse leak
Related terms
Leak rate
Quantity of gas entering a vacuum system through a leak per unit time, usually in mbar·L/s.
Hang-up
Helium that lingers in a leak detector or system after a big hit, holding the signal high and masking small leaks.
Helium bombing
Soaking sealed parts in pressurized helium so any leak lets helium in, then measuring how much comes back out.
Hold vacuum
Of a sealed system, to keep its pressure low with the pumps valved off; failing to hold means a leak.