The radial non-contact seals of the melt gear pump mainly include labyrinth seals, clearance seals, labyrinth clearance seals, spiral seals and labyrinth spiral seals, which are characterized by simple structure, durability, reliable operation, relatively low cost, convenient maintenance and suitable for various rotational speeds. It is suitable for shaft seal type of melt pump. The spiral seal and the clearance seal are both suitable for the sealing of high viscosity fluid. Although the clearance seal is easier to process than the spiral seal, there is no "pumping" effect of the spiral seal, and its sealing performance and reliability will be greatly affected. For this reason, screw seal has become the preferred method of polystyrene melt pump seal. In order to ensure the validity of pump shaft seal during shutdown or start-up, Butt Melt Pump Manufacturer adopts a new combination of screw seal and packing seal.