Multi-stage centrifugal pump

When taking it apart, the dimensions should be noted. New complex size

After aligning the flow channel of the primary impeller with that of the guide vanes, measure the axial height; then measure the height at the inlet dead center. The difference between these two heights is half the string length. When replacing the impeller without changing the shaft, dynamic balancing is required.

The new rotor must be fitted with V-blocks; the runout of the dial indicator on the ring should be within 0.1, and that of the shaft sleeve should be within 0.05. In December, we suffered losses due to maintenance issues: the new impeller had a vibration deviation of 0.3. The pump was disassembled while I wasn’t there, and it took me a week to grind it back to proper specifications. Also, the sequence and direction of each impeller shaft sleeve must be noted carefully; even a slight deviation can cause problems.

In such cases, the rotor assembly should be replaced. With such a long shaft, it’s difficult to ensure that it doesn’t deform during maintenance and replacement; on top of that, there’s the issue of shaft sleeve corrosion, as well as the need for dynamic balancing. Considering the costs involved, well, it’s not worth it. For reference.

The bearings on both sides are N308 type balls without an outer ring that allows sliding

Is it an AY-type multi-stage pump? It features packing seals on both sides, no positioning bearings, and N or NU series split rolling bearings on each side. This type of multi-stage pump does not require positioning and can achieve dynamic balance; as long as the balance pipes are not blocked, there are no problems. The balance disc and balance pipes are the main components used for balancing. The total shaft displacement and the additional displacement (i.e., half of the total displacement) need to be measured, with the additional displacement being half of the total displacement. Total clearance measurement method, Method 1: Measure the clearance of each impeller within the front and rear intermediate sections; the smallest value among all impellers represents the total clearance. If this total clearance is too large, adjust the clearance of the impeller with the smallest value accordingly. The total clearance can be determined using a depth gauge to measure the relative position of the impeller within these two intermediate sections. Specifically, when the front cover of the impeller is placed against the front intermediate section, the distance between the back cover of the impeller and the back intermediate section (the gap) constitutes the total clearance for that single impeller within the intermediate section. Method 2: Use the rotor and impeller. Once the intermediate sections have been installed one by one, and the shells of the inlet and outlet sections have been fitted along with all bolts tightened, the balance disc of the outlet section shell is removed. The rotor is then assembled, just as shown in the diagram for performing dynamic balancing. The bearing lock nuts are used to secure the bearings, while the stuffing box lock nuts are used to fasten the impellers, shaft sleeves, balance discs, and stuffing box sleeves together, thus forming a single unit – the rotor. After that, the rotor is pushed in the axial direction towards the inlet, causing it to shift axially. A depth gauge is used to measure the distance L1 from the balance disc to the outlet section shell. The rotor is then pulled back in the opposite direction, causing it to shift in the direction of the outlet; again, the distance from the balance disc to the outlet section shell is measured, giving L2. The total axial displacement L3 is therefore equal to L2 minus L1. To determine the additional displacement (half of the total displacement), the balance disc of the outlet section shell is reinstalled, and the rotor is assembled once more. The rotor is pushed towards the inlet side so that the surfaces of the two balance discs come into contact. The distance from the balance disc to the outlet section shell is measured, giving L4. The rotor is then pulled back in the opposite direction, and the distance from the balance disc to the outlet section shell is measured again, giving L5. The half-displacement L6 is then equal to L5 minus L4. If the half-displacement is greater than half of the total displacement, the shims behind the balance disc of the outlet section shell must be removed until the half-displacement reaches an appropriate value. If the half stroke amount is less than half of the total stroke, shims must be added behind the balance disk in the outlet section casing until the half stroke amount reaches the appropriate value.