a directional control valve , comprising : a valve body having a bore to receive a spool ; a spool mounted in said bore ; at least one stopper mounted in said bore , said stopper being axially adjustable and fixable at a selected axial position . the provision of an axially adjustable stopper eliminates the need to select a suitably sized stopper from a selection of stoppers or to grind down a single stopper . it reduces the number of parts in the valve and it also shortens the calibration time for the valve as there is no need to remove the stopper from inside the bore in order to perform an adjustment . as the valve is tested after each adjustment , this also means not removing the stopper and breaking the seal between each testing phase . the calibration can therefore be performed much more efficiently .