A device for dispensing a string or dab of liquid or plastic substance, such as putty, glue, paint or lubricant, to an object includes a pump for feeding the substance through a conduit to a nozzle having a fine discharge opening. A booster is connected to the conduit between the pump and the nozzle and a pressure medium is supplied to the booster. A substance control valve controls flow of the substance through the nozzle, the substance control valve being connected to the pressure medium and including a valve body which is biased in a closing direction by the substance and which is biased in an opening direction by the pressure medium via an actuator. The actuator includes a pressure member, one side of which is actuated by the pressure medium and the opposite side of which is actuated by the substance, the area of said pressure member being considerably larger than the area of said valve body. The device further includes a pressure medium control valve for controlling the substance control valve.