Abstract: The gun has a hollow grip (1) which incorporates an inlet duct (31), a substantially vertical on-off ball valve (26) occupying a central housing (C) and operated by a lever (3) recessed into the grip, and downstream of the on-off valve, a rotary valve (D) the central section (42) of which affords two sets of crossed holes (62, 63) offset from one another through 45.degree. and with their axes set in parallel longitudinal and vertical planes that also contain the axes of inlet and outlet galleries (37, 37', 38, 38') connecting the interior of the grip with respective spray and long-jet ducts (39, 41); the rotary valve turns as one with a ratchet mechanism (58, 51, 59) operated by a longitudinally disposed lever (4) that can be worked with the forefinger, independently of the on-off lever (3), which is squeezed by the remaining three fingers.