Tool for generating pulses in a flow of liquid passing through the tool, wherein: the tool includes a body (23, 54), and the body (23, 54) includes an inlet port and an outlet port, for conveying the liquid into and out of the tool; the tool includes a motor, and a rotor (25, 52), which is mounted in the body (23, 54) for motor-driven continuous rotation about an axis; the rotor (25, 52) has a curved-face, which is circular with respect to the axis of rotation; the tool includes an insert (40, 56), and includes an insert-guide; the insert-guide is structured to guide the insert for movement relative to the body (23, 54) towards and away from the rotor (25, 52), in a guided-direction; the guided-direction is either perpendicular to the axis of rotation or has a major perpendicular component; the insert (40, 56) has a curved-face, which is so profiled as to complement the curved-face of the rotor (25, 52); the insert (40, 56) includes a through-hole in its curved-face, termed the insert-aperture, which is open to a through-flow of liquid; the rotor (25, 52) includes a through-hole in its curved-face, termed the rotor-aperture, which is open to the through-flow of liquid; one of the apertures is connected to the inlet port and the other to the outlet port; the tool is so structured that, in operation, with the rotor (25, 52) rotating, and with liquid being passed through the tool under pressure, from the inlet port to the outlet port: the insert (40, 56) is biased into contact with the rotor (25, 52); the curved-face of the insert (40, 56) makes rubbing contact with the complementary curved-face of the rotor (25, 52), curved-face to curved-face; the rotor-aperture alternates cyclically, in time with the rotation of the rotor (25, 52), between being in liquid-flow-conducting alignment with the insert-aperture, and being out of alignment; a liquid-flow-conducting pulse-aperture opens between the rotor-aperture and the insert-aperture when the rotor-aperture and the insert-aperture are in alignment; the pulse-aperture alternately opens and closes, on a repeating cycle, in time with revolutions of the rotor (25, 52), whereby the liquid that emerges from the outlet-port emerges in cyclic pulses. the tool includes a body (23, 54), and the body (23, 54) includes an inlet port and an outlet port, for conveying the liquid into and out of the tool; the tool includes a motor, and a rotor (25, 52), which is mounted in the body (23, 54) for motor-driven continuous rotation about an axis; the rotor (25, 52) has a curved-face, which is circular with respect to the axis of rotation; the tool includes an insert (40, 56), and includes an insert-guide; the insert-guide is structured to guide the insert for movement relative to the body (23, 54) towards and away from the rotor (25, 52), in a guided-direction; the guided-direction is either perpendicular to the axis of rotation or has a major perpendicular component; the insert (40, 56) has a curved-face, which is so profiled as to complement the curved-face of the rotor (25, 52); the insert (40, 56) includes a through-hole in its curved-face, termed the insert-aperture, which is open to a through-flow of liquid; the rotor (25, 52) includes a through-hole in its curved-face, termed the rotor-aperture, which is open to the through-flow of liquid; one of the apertures is connected to the inlet port and the other to the outlet port; the tool is so structured that, in operation, with the rotor (25, 52) rotating, and with liquid being passed through the tool under pressure, from the inlet port to the outlet port: the insert (40, 56) is biased into contact with the rotor (25, 52); the curved-face of the insert (40, 56) makes rubbing contact with the complementary curved-face of the rotor (25, 52), curved-face to curved-face; the rotor-aperture alternates cyclically, in time with the rotation of the rotor (25, 52), between being in liquid-flow-conducting alignment with the insert-aperture, and being out of alignment; a liquid-flow-conducting pulse-aperture opens between the rotor-aperture and the insert-aperture when the rotor-aperture and the insert-aperture are in alignment; the pulse-aperture alternately opens and closes, on a repeating cycle, in time with revolutions of the rotor (25, 52), whereby the liquid that emerges from the outlet-port emerges in cyclic pulses. the insert (40, 56) is biased into contact with the rotor (25, 52); the curved-face of the insert (40, 56) makes rubbing contact with the complementary curved-face of the rotor (25, 52), curved-face to curved-face; the rotor-aperture alternates cyclically, in time with the rotation of the rotor (25, 52), between being in liquid-flow-conducting alignment with the insert-aperture, and being out of alignment; a liquid-flow-conducting pulse-aperture opens between the rotor-aperture and the insert-aperture when the rotor-aperture and the insert-aperture are in alignment; the pulse-aperture alternately opens and closes, on a repeating cycle, in time with revolutions of the rotor (25, 52), whereby the liquid that emerges from the outlet-port emerges in cyclic pulses.