Method for aligning the rotor assembly in multi-stage pumps

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During the assembly of multi-stage centrifugal pumps, there are many assembly techniques. Here is a brief introduction to the method for aligning the rotor components during the assembly of multi-stage pumps: An important issue in the assembly of multi-stage centrifugal pumps is to check whether the center of the impeller outlet coincides with the center of the inlet of the guide vanes; in other words, the centers of the impeller outlets must be aligned with the centers of the inlet ports of the guide vanes. Adjusting the \"center alignment\" not only ensures the proper efficiency of the pump but also prevents issues such as inability to rotate or wear between the impeller and surrounding components. “\"Centrical alignment\" is primarily determined by the position of the balance disc. As the pump operates, the balance disc moves back and forth, which directly affects the centrical alignment between the outlet of the impeller and the inlet of the guide vanes. Since the balance disc moves within a very small gap (usually 0.1–0.25 millimeters) relative to the balance ring while in operation, it automatically balances the axial forces. Therefore, checking and adjusting the \"center alignment\" can be carried out with the balance disc in close contact with the balance ring. "The condition for central alignment is: tightening the locking nut of the rotor and the tensioning bolts on the pump body, so that when the balance disk is in close contact with the balance ring, the outlet center of the impeller aligns with the inlet center of the guide vanes. During operation, since the gap between the balance disk and the balance ring is only about 0.1 millimeters, it can also be considered aligned. There are several methods for aligning the rotor assembly during the assembly of multi-stage centrifugal pumps. Method 1 for aligning the rotor assembly of a multi-stage centrifugal pump: 1. Insert the shaft, which already has the suction end sleeve and key, into the suction casing. 2. Install it into the first-stage impeller and impeller sleeve, ensuring that the impeller is in close contact with the front shaft sleeve. Then move the pump shaft so that the center of the outlet of the first-stage impeller coincides with the center of the inlet of the first-stage guide vane. At this point, make a mark on the shaft at the front end of the pump shaft, opposite to the end face of the packing gland, to facilitate checking the alignment of the impeller and the vanes later on. It should be noted that when adjusting the alignment between the outlet center of the first-stage impeller and the guide vanes, the impeller should be in close contact with the front shaft sleeve. At this time, the impeller cannot be pressed tightly against the suction shell. 3. After laying a layer of green-shell paper padding on the middle section, install the middle section and the second-stage impeller. Then, install the impeller shroud, the middle section, the third-stage impeller, and so on, up to the pump casing; attach the pump body bolts and nuts, and tighten the nuts. 4. Install the balance disc, and secure it using the shaft sleeve and the shaft sleeve locking nut. Press the balance disc tightly against the balance ring, and check the mark at the front end of the pump shaft; if the position of the mark remains unchanged, it indicates that the center of the outlet of the first-stage impeller is aligned with the center of the inlet of the first-stage guide vane. Since the impeller spacing and the vane spacing were measured and adjusted to be equal before assembly, each stage of impellers is aligned with its corresponding vanes. If the position of the mark changes, it indicates that the thickness of the gasket between the balance disc hub and the hub of the final impeller is not appropriate; adjusting the thickness of this gasket will resolve the issue. Second method for aligning the rotor assembly of multi-stage centrifugal pumps: Check and adjust by measuring the axial movement of the rotor. With the center of the impeller outlet aligned with the inlet of the guide vanes, there is an appropriate gap on both sides of the impeller. The range of movement on either side of the impeller before the balance disk is installed is referred to as the axial play of the rotor. After the balance disc is installed, with the balance disc in close contact with the balance ring, the rotor cannot move in the suction direction; it can only move in the discharge direction. Therefore, after installing the balance disc, check the axial play of the rotor; if it is equal to the specified value, it indicates good alignment ； If it is below the specified value, it indicates that the impeller is biased toward the discharge end ； If it is greater than the specified value, it indicates that the impeller is biased toward the suction side. Third method for aligning the rotor assembly of multi-stage centrifugal pumps: 1. Insert the shaft, equipped with the suction end sleeve and key, into the suction casing. 2. Install it into the first-stage impeller and impeller sleeve, ensuring that the impeller is in close contact with the front shaft sleeve. 3. After laying a layer of green-shell paper padding on the middle section, install the middle section and the second-stage impeller. Then, install the impeller shroud, the middle section, the third-stage impeller, and so on, up to the pump casing; attach the pump body bolts and nuts, and tighten the nuts symmetrically. Install a special sleeve with a length greater than the sum of the balance disc hub length and the total play, fit on the shaft sleeve, and secure it with a locking nut. 4. Move the rotor to the forward extreme, then mark the pump shaft using the end face of the front packing gland as a reference; subsequently move the rotor to the rear extreme and make another mark on the shaft at that reference point, in order to measure the total displacement. 5. After removing the retaining sleeve, install the balance disc and lock it in place. Press the balance disc tightly against the balance ring and make a mark on the shaft. Then pull the rotor back to the end point, and make a mark on the shaft. Measure the distance between the two marks; if it is equal to half of the total clearance, then the center of the impeller outlet coincides with the center of the vane inlet. Otherwise, the thickness of the gasket between the balance disk hub and the final impeller hub must be adjusted to meet the requirements. In multi-stage pumps with ball bearings at both ends, since the inner rings of the bearings are fixed to the shaft while the outer rings are supported on the bearing housing, the axial movement of the entire rotor is achieved through the sliding of the outer rings within the bearing housings. Therefore: 1. When disassembling multi-stage pumps that lack positioning shoulders on the shaft, the position of the front shaft sleeve must be marked to facilitate reassembly in its original state. 2. A clearance for axial movement must be provided between the protrusion of the bearing cover and the outer ring of the rolling bearing.