<p>This article presents a comparison of literature data and practical findings on single-stage hydro-ejector vacuum systems (HEVS), including information on the “dry” operation of the vacuum unit. Both analytical and empirical data on the dependence of vacuum on the working fluid temperature are considered. Results of pilot bench tests are presented, in which the maximum achievable vacuum level of a HEVS without an ejecting medium was determined. Existing methods for reducing the vapor pressure of the circulating working fluid are described and analyzed. The volume of ballast gas released at different water contents in the circulating working fluid is specified. The obtained theoretical and experimental data are compared with vacuum unit parameters at start-up and during “dry” operation. The maximum achievable vacuum level in conventional single-stage hydro-ejector vacuum systems is calculated. It is established that the principal limiting factor for a vacuum level is the presence of emulsified water in the working fluid.</p>