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 the mechanical seal and the treatment of the leakage of the water pump:
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.
01Common leakage phenomenon
The proportion of mechanical seal leakage accounts for more than 50% of all industrial water pump leakage. The operation of mechanical seal directly affects the normal operation of the water pump. The summary and analysis are as follows:
02Incentive for the sake of penetration
(1) Leakage due to pressure
1. Obstacle 1: Mechanical seal leakage caused by high pressure and pressure waves
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 too large, the liquid film will be difficult to form, the sealing end face will be worn more seriously, the heat will increase, and the sealing surface will be heated deformed.
Treatment method: When equipped with a mechanical seal, the amount of spring contraction must be carried out according to the regulations, and there should be no excessive or small phenomenon. 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: Mechanical seal leakage formed by vacuum operation
Cause: During the process of starting and stopping the pump, due to the congestion of the pump inlet and the presence of gas in the pumping medium, it may cause negative pressure in the sealing chamber. If there is negative pressure in the sealing chamber, it will lead to dry conflict on the sealing end face. Built-in type Air (water) leaks can occur from mechanical seals.
Treatment method: Equipped with double-end mechanical seal, which helps to improve the smooth condition and enhance the sealing function.
(2) Leakage due to 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 impurities
Cause: Solid particles enter the sealing end face, which will scratch or accelerate the wear of the sealing end face. The accumulation speed of scale and oil on the surface of the shaft (sleeve) exceeds the wear speed of the conflict pair, so that the moving ring cannot compensate for the wear displacement, and there is a hard-to-hard conflict. The operating life of the pair is longer than that of a hard-to-graphite conflict pair because solid particles become embedded in the sealing surface of the graphite seal ring.
Treatment method: The mechanical seal of tungsten carbide to tungsten carbide conflict pair should be selected at the position where solid particles can easily enter.
03
Mechanical seal leakage due to remaining issues
In the mechanical seal, there are still places where the design, selection, and installation are not correct.
(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 prevent damage to the dynamic and static ring seals.
The mechanical seal itself is a sophisticated component with high requirements, 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.
