1.

An automatic valve that opens or closes when an abnormal condition occurs (e.g., a pressure relief valve on a separator that opens if the pressure exceeds the set point, or the shutdown valve at the wellhead that closes if the line pressure becomes too high or too low).

2.

A valve installed at the top of the drill stem to prevent flow out of the drill pipe if a kick occurs during tripping operations.

A bearing between the walking beam and the sampson post of a pumping unit.

An influx of formation salt water into the wellbore