Mechanical seal, the cause and solution of liquid leakage

Mechanical seal, the cause of leakage and the solution Mechanical seal (mechanical seal) means that at least a pair of end faces perpendicular to the axis of rotation are maintained under the cooperation of the fluid pressure and the elastic force (or magnetic force) of the compensation tissue and the auxiliary seal. A device to prevent fluid leakage by combining relative sliding.　　 Introduce the reasons for the leakage of the mechanical seal and the treatment of the leakage of the water pump: 　　 Whether it is a self-priming pump, centrifugal pump, QW submersible sewage pump and other mechanical seals, it is the key reason for the leakage of industrial water pumps. Mechanical seal is also called end face seal. It has a pair of end faces perpendicular to the axis of rotation. Under the action of fluid pressure and compensating mechanical external elastic force, the end face relies on the cooperation of the auxiliary seal to maintain a fit with the other end, and relatively slide, thereby preventing fluid leakage. 01 Common leakage phenomenon The proportion of mechanical seal leakage accounted for more than 50% of all industrial water pump leakage. The performance of mechanical seals directly affects the normal operation of the pump. The summary and analysis are as follows: 　　02 Reasons for incentive penetration (1) ) Leakage caused by pressure 1. Obstacle 1: The mechanical seal leakage caused by high pressure and pressure wave is caused by: the design of spring specific pressure and total specific pressure is too large. When the pressure in the seal cavity exceeds 3MPa, the specific pressure of the seal end will be caused. If it is too large, it is difficult to form a liquid film, and the wear of the sealing end face is important, and the amount of fever increases, resulting in thermal deformation of the sealing surface.　　 Treatment method: When equipped with a mechanical seal, the amount of spring contraction must be carried out in accordance with the regulations, and there should be no excessive or small phenomena. The mechanical seal under high pressure should adopt countermeasures. In order to make the end face force correct, although the deformation is reduced, materials with high compressive strength such as cemented carbide and ceramic can be selected, and the smooth cooling countermeasures should be strengthened. 2. Obstacle 2: The mechanical seal leakage caused by the vacuum operation: during the start and stop of the pump, due to the congestion of the pump inlet and the gas in the pumped medium, it may cause negative pressure in the sealed cavity and the inside of the sealed cavity If there is a negative pressure, it will cause dry conflict between the seal end faces, and the built-in mechanical seal will leak air (water).　　 Treatment method: Equipped with a double-end mechanical seal, which helps to improve the smooth condition and enhance the sealing function.　　(2) Leakage caused by the medium 　　1. Obstacle 1: The auxiliary seals of the stationary ring and the moving ring are inelastic, and some may still ulcerate, resulting in a large amount of leakage of the mechanical seal and even the phenomenon of shaft grinding. Cause: The high temperature, weak acid and weak alkali in the sewage will corrode the static ring and the auxiliary rubber seal of the moving ring. The mechanical leakage is too large. The raw material of the moving and static ring rubber seals is nitrile -40. High temperature resistance, not acid and alkali resistance, easy to corrode when the sewage is acid and alkali.　　 Treatment method: For corrosive media, the rubber parts should be fluorine rubber resistant to high temperature, weak acid and weak alkali. 2. Obstacle 2: mechanical seal leakage caused by vacuum solid particles impurity: solid particles entering the seal end face will scratch or accelerate the wear of the seal end face, and the accumulation speed of scale and oil on the shaft (sleeve) surface exceeds that of the conflict pair. The wear rate causes the moving ring to be unable to compensate for the wear displacement. The operating life of the hard-to-hard collision pair is longer than that of the hard-to-graphite collision pair, because solid particles will be embedded in the sealing surface of the graphite sealing ring.　　 Treatment method: The mechanical seal of tungsten carbide to tungsten carbide collision pair should be selected at the position where the solid particles enter easily.　　03 　　Leakage of the mechanical seal due to other problems 　　There are still places where the design, selection, installation, etc. cannot be correct in the mechanical seal. (1) The amount of spring contraction must be carried out in accordance with the regulations, and there should be no excessive or too small phenomenon, deviation ±2mm, excessive contraction increases the specific pressure of the end face, excessive heat of conflict, and heat deformation of the sealing surface and accelerated end face wear , If the shrinkage is too small, the specific pressure of the dynamic and static ring end faces is insufficient, and the seal cannot be sealed.　　(2) The end face of the shaft (or sleeve) where the moving ring seal is installed and the end face of the sealing gland (or housing) where the static ring seal is installed should be chamfered and trimmed to avoid damage to the moving and static ring seals when equipped.　　The mechanical seal itself is a highly demanding and detailed component, which has high requirements on design, machining, and equipment quality. When using mechanical seals, the various factors of mechanical seals should be analyzed, so that the techniques of applying mechanical seals to various pumps must be discussed and the medium requirements must be adequately smooth, so as to ensure the long-term and reliable operation of the seal.