In the current work, a simple and low energy consuming system is proposed for holding on the vacuum in the steam power plant system. In this system, vacuum is created at the tip of an inverted U-pipe through which water flows by siphon effect. The stream of water through this pipe is brought about from a reservoir to another one whose water surfaces are at certain height difference. This height difference along with the height of the inverted U-pipe tip defines the value of the vacuum that can be produced. At this tip, the U-pipe is linked to the discharge pipe of a compressor which draws a mixture of air, non-condensable gases and some water vapor from the steam condenser and raises their pressure a little higher than that of the inverted U-pipe tip so that the resistance of connecting pipe is overcome and the pressure at exit of this pipe is equal to that at the inverted U-pipe tip. The mixture flows along with the water down the inverted U-pipe till it leaves the pipe with the water. A thermodynamic and fluid flow analysis is developed for predicting the performance of the proposed system. The results of this analysis show that the right selection of the mass flow rates ratio of water flowing in the inverted U-pipe and air and water vapor mixture sucked by the compressor from the steam plant condenser, in the range of 25000, the height of the inverted U-pipe summit from the water level of the higher water tank greater than 9.2 m and the height difference of the water levels in the two water tanks small enough, in the range of 0.1m saves the power of vacuum system by 80% less than that consumed when using compressor alone for venting the steam plant condenser.