Mechanical seals, causes and solutions for leakage

Mechanical seals, causes and solutions for leakage

Mechanical seal refers to the prevention of fluid leakage composed of at least a pair of end faces perpendicular to the rotation axis under the action of fluid pressure and compensation tissue elasticity (or magnetic force) and the cooperation of auxiliary seals to maintain fit and relative sliding. device. Introduce to everyone the reasons for the leakage of mechanical seals and the treatment methods for the leakage of water pumps: Whether it is 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, also known as end face seal, has a pair of end faces perpendicular to the axis of rotation. Under the action of fluid pressure and compensation of mechanical external elastic force, the end face relies on the cooperation of the auxiliary seal to maintain a close fit with the other end and slide relative to each other, thereby preventing fluid flow. leakage. 01 Common leakage phenomenon The proportion of mechanical seal leakage accounts for more than 50% of all industrial water pumps. The operation of the mechanical seal directly affects the normal operation of the water pump. The summary and analysis are as follows: 02 Reasons for incentive penetration (1 ) Leakage caused by pressure 1. Obstacle 1: Leakage of mechanical seal caused by high pressure and pressure wave Cause: The spring specific pressure and total specific pressure are designed too large. When the pressure in the sealing chamber exceeds 3MPa, the specific pressure of the sealing end face will be increased. If it is too large, it will be difficult to form a liquid film, the sealing end face will be worn, and the amount of heat will increase, resulting in thermal deformation of the sealing surface. Treatment method: When equipped with a mechanical seal, the spring shrinkage must be carried out according to the regulations, and there should not be too large or too small phenomena. The mechanical seal under high pressure conditions should take countermeasures. In order to make the force on the end face correct, even if the deformation is reduced, materials with high compressive strength such as cemented carbide and ceramics can be selected, and the cooling measures can be strengthened. 2. Obstacle 2: The leakage of the mechanical seal formed by the operation of the vacuum state occurs: During the startup and shutdown of the pump, due to the congestion of the pump inlet and the gas contained in the pumping medium, it may cause negative pressure in the sealed cavity, and the inside of the sealed cavity may become negative. If there is a negative pressure, it will cause dry conflict on the sealing end face, and the built-in mechanical seal will leak air (water). Treatment method: Equipped with 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 static ring and the moving ring are inelastic or some are still festering, resulting in a large amount of leakage of the mechanical seal and even the phenomenon of shaft grinding. Cause: High temperature, weak acid and weak base in sewage erode the static ring and the auxiliary rubber seal of the moving ring, resulting in excessive mechanical leakage. The raw material of the rubber sealing ring of the dynamic and static rings is nitrile-40, which is not High temperature resistance, not acid and alkali resistance, easy to corrode when the sewage is acid and alkali. Treatment method: For aggressive media, the rubber parts should be fluororubber resistant to high temperature, weak acid and weak alkali. 2. Obstacle 2: Mechanical seal leakage caused by vacuum solid particles and impurities: Solid particles entering the sealing end face will scratch or accelerate the wear of the sealing end face, and the accumulation speed of scale and oil on the surface of the shaft (sleeve) exceeds the speed of the conflict pair. The wear rate causes the moving ring to fail to compensate for the wear displacement. The operating life of the hard-to-hard contact pair is longer than that of the hard-to-graphite contact pair, because solid particles will embed in the sealing surface of the graphite sealing ring. Treatment method: The mechanical seal of the tungsten carbide-tungsten carbide conflict pair should be selected at the position where the solid particles can easily enter. 03 Leakage of mechanical seal caused by other problems There are still places where design, selection, installation, etc. cannot be correct in the mechanical seal. (1) The amount of spring contraction must be carried out according to the regulations, and there should not be too large or too small phenomenon. The deviation is ±2mm. If the amount of contraction is too large, the specific pressure of the end face will be increased, and the conflicting heat will be too much, resulting in thermal deformation of the sealing surface and accelerated wear of the end face. , If the shrinkage is too small, the end face of the dynamic and static rings is insufficient, and it cannot be sealed. (2) The end face of the shaft (or shaft sleeve) on which the dynamic ring seal is installed and the end face of the sealing gland (or housing) on ​​which the static ring seal is installed should be chamfered and trimmed to avoid damage to the dynamic and static ring seals. The mechanical seal itself is a high-demanding and careful component, which has high requirements for design, machining, and equipment quality. When using mechanical seals, various factors for the use of mechanical seals should be analyzed, so that the technical requirements for the use of mechanical seals in various pumps and the use of medium requirements and sufficient smooth conditions can ensure long-term reliable operation of the seals.