Gas distribution apparatus to provide uniform flows of gases from a single source to multiple processing chambers are described. A valve upstream of a shared volume is controlled by at least two pressurizing sequences during a process it the processing chamber. The first pressurizing sequence opens and closes the upstream valve a first number of cycles and the second pressurizing sequence opens and closes the upstream valve less frequently after the first number of cycles. The open/close timing of the second pressurizing sequence occurs less frequently than the open/close timing of the first pressurizing sequence.