A gas panel according to various aspects of the present invention is configured to deliver a constant flow rate of gases to a reaction chamber during a deposition process step. In one embodiment, the gas panel comprises a deposition sub-panel having a deposition injection line, a deposition vent line, and at least one deposition process gas line. The deposition injection line supplies a mass flow rate of a carrier gas to a reactor chamber. Each deposition process gas line may include a pair of switching valves that are configured to selectively direct a deposition process gas to the reactor chamber or a vent line. The deposition vent line also includes a switching valve configured to selectively direct a second mass flow rate of the carrier gas that is equal to the sum of the mass flow rate for all of the deposition process gases to the reactor chamber or a vent line. The gas panel is configured to substitute the mass flow rate of the deposition vent line with the mass flow rate of the deposition process lines, such that when the deposition vent line is directed to the reactor chamber the deposition process lines are directed to the vent line and when the deposition vent line is directed to the vent line the deposition process lines are directed to the reactor chamber. The substitution of the two mass flow rates maintains a constant mass flow rate of gases to the reactor chamber throughout the deposition process step.