求翻译：由于真空系统的真空度不恒定，在一定间隔内变化，所以用水量也应该呈现一定的变化。随着真空度的递减，用水量作相应的增加；当到达临界值（设定值P=0.02 MPa）时真空泵动作，使真空储存罐的真空度升高，直至P=0.03 MPa，此时需要真空储存罐的体积较大，以保证真空泵不必频繁的启动，以节省电能是什么意思？

Because of the vacuum system of vacuum is not constant, changes within a certain interval, so water consumption should also render some changes. With the decline of vacuum, water consumption increased accordingly when reaches the critical value (setpoint P=0.02 MPa) vacuum pump when the action, the vacuum storage tank vacuum up until P=0.03 MPa, require vacuum storage tank volume is large, to ensure that the vacuum pump without frequent startup, to save power