Abstract: An LPCVD system is provided in which a mass flow controller is used to control the flow rate of gases passing from a reaction chamber to a vacuum pump. The mass flow controller is disposed within a secondary outlet conduit which connects a first point to a second point of a primary outlet conduit. The primary outlet conduit extends between and in gaseous communication with the reaction chamber and the vacuum pump. The secondary outlet conduit permits gases flowing from the reaction chamber to bypass a primary valve disposed within the outlet conduit downstream of the first point and upstream of the second point. The mass flow controller can advantageously maintain the flow rate of the gases at a setpoint value for a period of time before the flow rate begins to drop. As such, the mass flow controller provides for a reduction in the time required to evacuate the vacuum chamber.