A carrier fluid with entrained particulate solid material (14), for abrasive purposes, is fed through an inlet (12) in a housing (3) so as to follow a spiral path, thereby preventing the particulate solid material (14) from settling under the influence of gravity. The housing (3) defines a transfer space (5) which is bounded, in part, by a first end (18) and a second end (20) of the housing (3). The fluid with the entrained particulate solid material (14) is deflected inwardly by the inner surfaces (15 and 16) of the first and second ends (18 and 20) of the housing (3) into a liquid jet (11) issuing from a jetting nozzle (9) in the first end (18) of the housing (3). The particulate solid material (14) is thereby entrained in the outer layer of the jet (11) issuing from an outlet aperture (8) in the second end (20) of the housing ( 3), thus enabling the jet (11) to be used for cutting or cleaning purposes.