In an embodiment, a fluid ejection device includes a die substrate having first and second fluid slots along opposite substrate sides and separated by a substrate central region. First and second internal columns of closed chambers are associated with the first and second slots, respectively, and the internal columns are separated by the central region. Fluidic channels extending across the central region fluidically couple closed chambers from the first internal column with closed chambers from the second internal column. Pump actuators in each closed chamber pump fluid through the channels from slot to slot.