Basic knowledge of mechanical seals

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I. Basic knowledge of mechanical seals: 1. Basic concept of mechanical seals: A mechanical seal is a device designed to prevent fluid leakage, consisting of at least one pair of end faces perpendicular to the axis of rotation, which remain in close contact and slide relative to each other under the action of fluid pressure and the elastic force (or magnetic force) of a compensation mechanism, as well as with the assistance of additional sealing elements. A mechanical seal in which the auxiliary seal of the compensation ring is a metal bellows is called a bellows mechanical seal. 　 2. Components of a mechanical seal: It mainly consists of the following four types of components. a. Main seals: rotating ring and stationary ring. b. Auxiliary seals: sealing rings. c. Compression elements: springs, push rings. d. Transmission components: spring basket seat and keys or fixing screws. II. Points to note regarding the operation of the mechanical seal: 1. Precautions during installation a. Great care must be taken to avoid any installation errors. (1) Tightening the gland should be done after the coupling has been aligned; the bolts should be tightened evenly to prevent the gland surface from becoming skewed. Use a feeler gauge to check each point, ensuring that the error is no more than 0.05 millimeters. (2) Check the clearance between the gland and the outer diameter of the shaft or bushing (i.e., their concentricity). The clearance should be uniform all around; using a feeler gauge, verify that the tolerance at each point does not exceed 0.01 mm. 　 b、The compression amount of the spring must be in accordance with the specified values; it is not allowed to be too large or too small, with an allowable error of 2.00 millimeters. Excessive size increases the specific pressure on the end face, thereby accelerating its wear. If it is too small, the specific pressure will be insufficient to provide a sealing effect. 　　 c. After the moving ring is installed, it must be able to move freely on the shaft; when pressed against the spring, it should be able to spring back automatically. 　　 2. Precautions during disassembly a. Be careful when removing the mechanical seal; it is strictly prohibited to use hammers or spades to avoid damaging the sealing elements. A pair of wire hooks can be made, which are inserted into the notch in the drive seat in the direction that corresponds to the self-profit-and-loss mechanism, in order to pull out the sealing device. If the scale cannot be removed, it should be cleaned thoroughly before attempting to remove it. 　 b. If mechanical seals are used at both ends of the pump, care should be taken during assembly and disassembly to avoid neglecting one aspect while focusing on another. 　 c. For used mechanical seals, in cases where the gland has become loose, causing the seal to shift, the stationary and rotating ring components must be replaced; they should not be retightened and reused. Because after such movement of the columns, the original operating path of the friction pair changes, which easily leads to a breakdown in the sealing performance of the contact surface. 　 III. Normal operation and maintenance issues of mechanical seals: 1. Pre-start preparations and precautions a. Conduct a comprehensive inspection to ensure that the mechanical seal, as well as all auxiliary devices and pipelines, are properly installed and meet the technical requirements. 　 b. Perform a hydrostatic test on the mechanical seal before starting it, to check for any leakage. If there is significant leakage, the cause should be identified and steps taken to eliminate it. If it still doesn’t work, it should be disassembled for inspection and reinstalled. Generally, the hydrostatic test pressure is set at 2–3 kg/cm². 　 c. Rotate the pump according to its rotation direction to check whether it turns smoothly and evenly. If the turntable struggles to rotate or does not move, check whether the assembly dimensions are incorrect and whether the installation is proper. 　 2. Installation and Shutdown a. The sealing chamber should be kept filled with liquid before starting up. When transporting a solidified medium, steam should be used to heat the sealed chamber in order to melt the medium. The shaft must be turned before starting to prevent the soft ring from breaking due to sudden startup. 　b. For mechanical seals that utilize an external seal oil system, the seal oil system should be started first. After stopping, finally shut down the oil sealing system. 　c. After the hot oil pump is shut down, the cooling water used to cool the oil seal chamber and the face seal should not be stopped immediately; it should only be ceased once the oil temperature at the face seal drops below 80 degrees, in order to avoid damaging the sealing components. 　 3. Operation a: If there is a slight leak after the pump starts, observe it for some time. If the leakage does not decrease after 4 hours of continuous operation, the pump should be stopped for inspection. b. The operating pressure of the pump should be stable, with pressure fluctuations not exceeding 1 kilogram per square centimeter. c. During operation, the pump should be prevented from experiencing vacuum conditions, to avoid dry friction at the sealing surfaces and seal damage. d. The sealing condition should be checked regularly. During operation, if the leakage exceeds the specified limits – no more than 5 drops per minute for heavy oil and no more than 10 drops per minute for light oil – and there is no improvement within 2–3 days, the pump should be stopped to inspect the sealing mechanism.