A system for evacuating a reactor chamber includes a main evacuation line connected at one end thereof to the reactor chamber and at another end thereof to a means for creating a partial vacuum. A valve in the main evacuation line divides the line into a chamber side and a vacuum side. A second line is connected at one end to the vacuum side of the main evacuation line and at another end to a fluid supply source. As the valve in the main evacuation line is opened, fluid is supplied through the second line to the main evacuation line to prevent rapid, turbulence-inducing pressure drops in the reactor chamber.