An arrangement for a control valve for controlling pressure and flow rate of a fluid, the fluid flowing via an inlet into the control valve being brought to rotate about a main flow axis before the fluid, at least with reduced pressure or speed energy, flows via an outlet opening from the control valve and where at least one inlet port communicating with the inlet being provided tangentially in relation to an inlet portion of the speed reduction chamber located in the control valve, and where the speed reduction chamber, provided substantially concentric with the main flow axis, is divergent over at least the first portion of the main flow direction.