In the current work, a simple and low energy consuming system is proposed for holding on the vacuum in the steam power plant system. The vacuum is created at the tip of an inverted U-pipe through which water flows by siphon effect due to the height difference in water surfaces of two tanks. This height difference and the elevation of the inverted U-pipe tip define the value of the vacuum to be grown. The U-pipe tip is connected to the discharge pipe of a compressor which draws a mixture of air, and water vapor from the steam condenser and raises their pressure a little higher than that of the inverted U-pipe tip. The mixture flows with the water down the inverted U-pipe till they depart the U-tube. 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 flowrate ratio of water flowing in the inverted U-pipe to air and water vapor mixture sucked by the compressor from the steam plant condenser, in the range of 25,000, 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 0.1 m saves the power of vacuum system by 80% less than that consumed when using compressor alone for venting the steam plant condenser.