Methods and systems for pumping fluid through tubing are provided. Methods include orbiting one or more first rollers at multiple angular speeds around the periphery of a substantially circular first disk having a first radius with each first roller travelling at the same angular speed as the other first rollers, orbiting second rollers at a second angular speed around a substantially circular second disk having substantially the first radius, and increasing the pressure of fluid in tubing between one first roller and one second roller by causing the one or more first rollers to orbit at a first angular speed greater than the second angular speed so the one first roller moves along and fully compresses the tubing in a first section of the first disk, and simultaneously causing the one second roller to move along and fully compress the tubing in a first section of the second disk.