Increase something by a small amount, especially after a series of increases, or to increase in this way. "Raising the minimum wage would ratchet up real incomes in general."; "The debate will ratchet up a notch on Wednesday when the Commission publishes its report."
If something ratchets up or is ratcheted up, it increases by a fixed amount or degree, and seems unlikely to decrease again. an attempt to ratchet up the pressure He fears inflation will ratchet up as the year ends ratchet down