Working principle of mechanical seal Mechanical seal

Working principle of mechanical seal




2019-07-26 16:38





1. Structure, generally composed of moving ring, static ring, moving ring sealing ring, static ring sealing ring, spring, spring seat, set screw, anti-rotation pin, etc. Mechanical seals generally have four sealing points, of which 3 are the sealing points between the static ring and the end face of the gland, 2 are the sealing points between the moving ring and the shaft or bushing, and 4 are the sealing points between the stationary ring and the gland end face. It is the sealing point between the gland and the pump casing or other equipment, 1  It is the sealing point where the end face rotates relative to each other. 2, 3, and 4 are static seals, which are usually sealed by gaskets such as O-shaped and V-shaped sealing rings. 2. Principle       When the mechanical seal is working, the axial force caused by the pressure of the sealing fluid and the elastic force of the elastic element makes the moving ring and the static ring fit and move relative to each other. Due to the tight fit of the two sealing end faces, the junction between the sealing end faces ( Sealing interface) forms a small gap, when the pressurized medium passes through this gap, an extremely thin liquid film is formed, which produces resistance and prevents the medium from leaking. 3. Classification  (1) Main engine according to seal: mechanical seals for pumps, mechanical seals for kettles, mechanical seals for compressors, etc.;  (2) According to different working parameters, it is divided into high temperature, medium temperature, low temperature, high pressure, medium pressure, low pressure, high speed, heavy duty, etc.;  (3) According to the structural form, it is divided into: balanced type and unbalanced type, single-end and double-end mechanical seals, etc.  4. Install (1) Preparation  ① Check whether the radial runout, surface roughness, outer diameter tolerance, and shaft movement of the shaft and sleeve meet the accuracy requirements;  ② Check whether the model and specification of the mechanical seal meet the requirements. Whether the parts are in good condition, whether the size of the sealing ring is appropriate, whether the surface of the moving ring and the static ring is smooth and flat. If defective it must be replaced or repaired.  ③Clean the parts of the mechanical seal with clean gasoline, then dry it, and pay attention to protect the sealing surface;  ④ When installing the mechanical seal, first check the working length of the spring from the manual, and then use a caliper to measure the free length of the spring to obtain the compression of the spring. During installation, ensure that the deviation of the compression of the spring is not greater than 1mm. (2) Inspection and measurement  ① The floating of the moving ring requires a certain gap between the moving ring and the shaft, and the gap is guaranteed to be 0.3-0.7mm.  ②Whether the fixing ring is eccentric   In the mechanical seal for pumps, the fixed ring (spring seat) and the shaft adopt a sliding fit, and the clearance is very small. If the gap is large, the fixed ring will be eccentric, and the spring force acting on the sealing surface will be uneven, and the seal will leak and seal when the seal occurs.  ③Inspection of the bonding surface between the moving ring and the static ring: 90% can be used for inspection° The square measures the deviation from the shaft centerline of the mating face. First, assemble the parts of the rotating assembly and the static ring assembly respectively, and pre-tighten the spring; then complete the installation of the moving ring assembly on the shaft and the installation of the static ring assembly in the gland, and conduct preliminary measurements The difference between the distance from the end face of the moving ring seal to the end face of the seal chamber and the distance from the seal face of the stationary ring to the end face of the end cover is the spring pre-compression of the mechanical seal, and the bearing is assembled; compare the compression amount required by the technical requirements, refer to According to the measured compression amount, adjust the compression amount appropriately and tighten the gland.    During the installation process, the seal should be kept clean and intact, and it is not allowed to hit the sealing element with tools to prevent the seal from being damaged. After the mechanical seal is installed on the shaft, push the moving ring by hand to feel elastic and smooth, then add some engine oil on the sealing surface, and press the end cover evenly without deviation. (4) Inspection and pressure test     After the installation is completed, turn the car by hand to ensure flexible rotation and a certain degree of floating. The mechanical seals of important equipment must undergo static pressure tests and dynamic pressure tests, and they can be put into formal use only after passing the tests. 5. run  (1) Precautions before starting: whether the auxiliary device and cooling system are installed correctly; the pipeline should be cleaned to prevent rust and impurities from entering the sealing chamber; turn the coupling by hand to check whether the shaft runs easily. If the disc is very heavy, check whether the matching dimensions are correct, try to find out the cause and troubleshoot.  (2) Trial operation and normal operation: first start the liquid seal system and cooling water system to fill the sealing cavity with medium, then start the main seal for trial operation.