(57) In a system for supplying fluid to a printing roller for lithographic printing, an infra-red thermometer is provided for sensing the temperature of the printing roller (38) surface. A control device is provided and controls a cooling unit for air pumped from a pump (30) dependent upon the temperature sensed by the thermometer. The cooled air is directed onto the printing cylinder (38) by a fluid supply device (10) which comprises a cylindrical tube (11) having aligned outlet openings (12) along its length. Each outlet opening (12) is elongate in the axial direction and has rounded corners. The tube (11) includes a filter unit (29) and a needle valve (28) at the end opposite the inlet and has a baffle plate (26) running axially therethrough. These features inhibit turbulence in the tube (11). There is a compensation opening (18) on the other side of the tube to each outlet opening (12) and each compensation opening (18) is the same size as its opposite outlet opening (12). Throttle clips (14) are provided on the tube (11) and allow the outlet openings (12) to be open when the compensation openings (18) are closed and the compensation openings (18) to be open when the outlet openings (12) are closed.