Abstract: A hot melt adhesive applicator including a dispenser head or block having a liquid chamber in one end portion and a cartridge cavity in the opposite end portion communicating through a stem passage and further comprising a replacable needle valve cartridge including a valve body containing a pneumatically actuated valve having a valve stem depending below the valve cartridge body through the stem passage and the liquid chamber for opening and closing the orifice in the nozzle assembly at one end of the liquid chamber. The dispenser head or block is modular and adapted to receive one or more valve cartridges and is provided with a liquid passage communicating with the liquid chamber and a source of liquid under pressure, and an air passage communicating with the air chamber in the cartridge within the cartridge cavity and also communicating with a source of compressed air. The dispenser head is preferably heated in order to maintain the hot melt adhesive in the liquid chamber in a liquid condition.