Abstract: A liquid-propelled abrasive cleaning apparatus comprising a nozzle for applying a high pressure stream of water and propelled sand particles to a surface to be cleaned; a pump for furnishing water under high pressure to the nozzle, the pump being of a kind which may be driven by a pressurized fluid medium and having a discharge outlet; a first conduit for connecting the outlet to the nozzle; a second conduit for delivering the medium to the pump; a normally closed valve in the first conduit; a pneumatic actuator for opening the valve; and a control device disposed in proximity with the nozzle for enabling pressure to be applied to the actuator to open the valve only when the nozzle is in use.