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Methods for aligning and centering the coupling between the water pump and the motor 1. The importance of pump alignment The rotation centers of the two shafts connected by the coupling between the pump and the motor must be strictly concentric; the coupling must be accurately aligned and centered during installation. Otherwise, significant stress will be generated in the coupling, which will severely affect the proper functioning of the shafts, bearings, and other components on the shafts. This can even lead to vibrations or damage to the entire machine as well as its foundation. Therefore, the alignment of the pump and motor coupling is one of the very important steps in the installation and maintenance process. 2. Alignment of the coupling – analysis of offset conditions When installing a new pump, it is not necessary to check the perpendicularity between the coupling’s end face and the axis; however, when installing an old pump, this must be checked carefully. If there is any deviation from perpendicularity, it must be corrected before proceeding with alignment. Under normal circumstances, the following four situations may arise. 1) When S1=S2 and a1=a2, the end faces of the two backrest wheels are in the correct position, being both parallel and concentric; under these conditions, the two axes must lie on the same straight line. 2) When S1=S2 and a1≠a2, the end faces of the two backrest wheels are parallel but their axes are not aligned; in this case, there is a parallel radial displacement e=(a2-a1)/2 between the two axes. 3) When S1≠S2 and a1=a2, the end faces of the two backrest wheels are concentric but not parallel, with an angular displacement α between their axes. 4) Since S1≠S2 and a1≠a2, the end faces of the two backrest wheels are neither concentric nor parallel; there is both a radial displacement e and an angular displacement α between the two axes. The coupling is in the first condition, which is the state we strive to achieve during alignment; whereas the second, third, and fourth conditions are all incorrect, and adjustments are needed to bring it back to the first condition. When installing the equipment, first install the driven unit (pump) with its axis in a horizontal position, and then install the driving unit (motor). Therefore, for alignment, it is sufficient to adjust the driving unit by using adjustment shims under its support feet. 3. Measurement and adjustment methods during alignment The following mainly introduces two commonly used measurement and adjustment methods during maintenance. Depending on the measuring tools used, they can be classified as follows: 1) Using a blade gauge and feeler gauge to measure the misalignment of the coupling, and using a wedge-shaped gap gauge or feeler gauge to measure the lack of parallelism in the coupling’s end faces. This method is suitable for equipment with elastic connections that operates at low speeds and where high precision is not required. 2) Use a dial indicator along with a stand or specialized alignment tool to measure the misalignment and lack of parallelism between the two couplings. This method is suitable for rotating equipment with high speeds, rigid connections, and high precision requirements. Note: 1) When using feeler gauges and blade rulers for alignment, the surface of the radial end face of the coupling should be flat, smooth, free of rust, and free of burrs. 2) To see the light from the knife-shaped ruler clearly, it is best to use a flashlight. 3) For the final measurement, the motor’s foot bolts must be fully tightened, with none being loose. 4) When using special tools for alignment, make the same mark; to avoid increased errors in the measurement data, the back wheel should be divided into 4–8 points to obtain accurate readings. 5) Keeping records is an important part of alignment. The following methods are used when adding adjustment shims: 1) Visual (empirical) method (adding or removing shims based on experience). Since during maintenance, optimal conditions and tools are not always available for aligning certain pumps, the experience of experienced workers plays a crucial role in this process (each time shims are added or removed, it is necessary to consider the tightness of the motor bolts as well as any remaining clearance). 2) Calculation method I Original state II Elevation by Δh III Adjusted axis line (1) First, eliminate the height difference of the coupling. The motor shaft should be elevated by Δh using shims; therefore, both the front support A and the rear support B should have Δh of shims added under them. (2) Eliminate the gap in the coupling: Add shims of different thicknesses under supports A and B; the shim placed under support B should be positioned further back than that under support A. Is GF equal to FH? ? ? The total thickness of the adjustment shims is: front support A: Δh+AC; rear support B: Δh+BD. Standard for centering deviation of water pump couplings (unit: mm) Distance between the end faces of water pump couplings