Question 39General Subjects - 1st Asst/Chief

The correct answer is C) by an external line from the first stage via a fixed orifice. In a flash-type evaporator, the vacuum in the salt water feed heater shell is generally maintained by an external line that connects the first stage of the evaporator to the feed heater shell. This external line includes a fixed orifice, which helps create the necessary vacuum in the feed heater shell by drawing vapor from the first stage. The other options are incorrect because: A) the fixed orifice is typically used to control the steam supply, not create the vacuum; B) there is no direct unimpeded connection between the second stage and the feed heater; and D) a separate air ejector unit is not the primary means of creating the vacuum in the feed heater shell.