A small quantity of uncondensible gases will tend to build up in the tower and the surface condenser which, if allowed to build up, will slowly destroy the vacuum.
The ejector is used to remove the uncondensibles which are passed into the separator after passing through the ejector condenser which condenses the ejector steam – thus helping to maintain the vacuum, while the uncondensed gases are fed via a check-valve or control valve to atmosphere or flare system. The barometric seal loop holds a head of liquid which will prevent the vacuum pulling gases back out of the separator.