A gas phase introduced into a vessel above a liquid phase to prevent contamination of the liquid, reduce hazard of detonation, or to exert pressure on the liquid. Also known as cushion gas.

Related Terms


Mechanical process vessel with wettable, high-surface area packing on which liquid droplets consolidate for gravity separation from a second phase (for example, gas or immiscible liquid).


The gas pressure at which a system is at its dew point, that is, the conditions of gas temperature and pressure at which the first dew or liquid phase occurs.


The physical geometry exhibited by a multiphase flow in a conduit; for example, liquid occupying the bottom of the conduit with the gas phase flowing above, or a liquid phase with bubbles of gas.


The cross-sectional area locally occupied by the gas phase of a multiphase flow, relative to the cross-sectional area of the conduit at the same local position.


A separator that utilizes subatmospheric pressure to remove certain gases and liquids from another liquid because of their difference in vapor pressure.


A filled-system temperature-measurement device in which gas or liquid enclosed within the device responds to heat by a volume change (rising or falling of mercury column) or by a pressure change (opening or closing of spiral coil).


On a PVT phase diagram, the line that separates the two-phase (gas-liquid) region from the one-phase (gas) region, and indicates the point at a given gas temperature or pressure at which the first dew or liquidphaseoccurs.


  1. A modified U-tube manometer used to measure draft of low gas heads, such as draft pressure in a furnace, or small differential pressures, for example, less than 2 inches (5 centimeters) of water. 2. A hydrostatic depth indicator, installed in the side of a vessel below the light load line, to indicate amount of submergence.


The force exerted by a liquid or gas on a unit area. Three pressures may be involved: gauge pressure, the unit pressure above atmospheric pressure; absolute pressure, gauge pressure plus the atmospheric pressure; vacuum pressure; the pressure below atmospheric pressure usually expressed in inches of Hg.


  1. Volume of material held or contained in a process vessel or line. 2. Liquid held up (suspended) in a vertical process vessel or line by rising gas or vapor streams.

Related questions

MarineProHelp 2018 - 2019.