An aspect of the invention refers to a system for cleaning an external vehicle-mounted sensor surface. The system comprises an air nozzle arranged to discharge air onto a sensor surface; an air pump comprising a fluid inlet, an air outlet, an air-fluid interface and a variable volume compression chamber communicated with the air outlet; an air flow control device communicated with the air nozzle and the air outlet for controlling the flow of air therethrough; and a liquid pump communicated with the fluid inlet to supply a flow of pressurized liquid such that the volume of the compression chamber varies to generate a volume of pressurized air with an absolute pressure below 10 bar.