Common mistakes in the maintenance of mechanical seals

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This post was last edited by Thank goodness you're here on 2016-3-3 at 14:46. Points to note when operating mechanical seals: 1. Precautions during the installation of mechanical seals: 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 fit clearance between the gland and the outer diameter of the shaft or sleeve (i.e., the degree of concentricity); it should be uniform around the perimeter. Use a feeler gauge to ensure that the tolerance at each point is no more than 0.01 millimeters. 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. An excessive value will increase the end-face specific pressure and accelerate end-face 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 when removing the mechanical seal: 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 mechanically sealed units that have been in operation and where the gland loosening has caused the seal to shift, the stationary and rotating ring components must be replaced; they should not be retightened and used again. Problems related to the normal operation and maintenance of mechanical seals: 1. Preparatory work and precautions before starting a mechanical seal a. Thoroughly inspect the mechanical seal, as well as the auxiliary devices and pipelines, to ensure that they are all in place 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 addressed to eliminate it. If it still doesn’t work, it should be disassembled for inspection and reinstalled. The typical hydrostatic test pressure is 2 to 3 kilograms per square centimeter. c. Turn the pump by hand according to its rotation direction to check whether it turns smoothly and evenly. If the turning gear struggles to rotate or does not move, check whether the assembly dimensions are incorrect and whether the installation is proper. 2. Installation and shutdown of mechanical seals a. The seal chamber should be kept filled with liquid before startup. 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 parking, stop the oil sealing system last. 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 of mechanical seal a. If there is slight leakage 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. While the pump is in operation, cavitation should be avoided to prevent dry friction on the sealing surfaces and damage to the seals. 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.