Adjustment of the axial shift in multi-stage centrifugal pumps?

“After the partition was assembled, the total rearward displacement was 7.8 millimeters; after installing the balance disc, the rearward displacement measured at 5.5 millimeters. This indicates that the gap in the balance disc is too large. It is necessary to add shims on the back side of the balance ring (if it is adjustable), or replace it with a balance disc of larger axial dimensions, while removing shims from the back side of the balance disc.

Personal understanding: This situation indicates that too few shims have been used; it is necessary to remove some shims between the balance disc and the shaft shoulder. Since it is a hot oil pump, it is essential to ensure that the thermal expansion amount on the front side is 0.5 mm greater than that on the back side (4.15 mm on the front vs. 3.65 mm on the back). Therefore, 1.85 mm of shims need to be removed (5.5 – 3.65).

Can you write out your calculation process? Thank you

Vibration compensation is intended to ensure that the center of the impeller’s flow channel aligns as closely as possible with the center of the pump casing’s flow channel during operation, thereby improving the pump’s efficiency. The total stroke is the total distance by which the centerline of the impeller can move within the pump casing. During installation, the half stroke is determined by the balance disc: before installing the balance disc, the rotor is pushed to the bottom, and after the balance disc is in place, it is pushed to the bottom again; the amount by which the rotor is pulled out after installing the balance disc represents the half stroke. Theoretically, the half stroke is half of the total stroke, with the centerline of the impeller coinciding exactly with the centerline of the flow channel. However, in operation the balance disc does not remain on its installed positioning plane, and due to thermal expansion, the half stroke may deviate slightly from the theoretical value during installation. Based on the total displacement, and the fact that the displacement in the front is 0.5 more than that in the back, the displacements in the front and back can be calculated as 4.15 and 3.65 respectively. However, the actual displacement in the back is 5.5; therefore, a shim of 5.5 – 3.65 = 1.85 mm needs to be used

The adjustment is related to the shims on the thrust side; there should be specified requirements for the total play after installation in the drawings. The 0.5 value mentioned refers only to a difference, and there is a required minimum value for each side. Generally, a value of 5.5 is sufficient; by adjusting the thickness of the shims on the thrust side, it is possible to achieve the desired difference between the front and back positions. Although you have reduced the number of shims used for the balance disk, once the thrust bearings are installed, it’s not guaranteed that the rotor will be exactly in the center. Ultimately, the clearance still needs to be adjusted using the thrust bearings. Therefore, to adjust the clearance on the thrust side, it is necessary to measure the half-shift of the rotor after installing the thrust bearings

I just don’t understand how 4.15 and 3.65 were calculated

Based on your total runout of 7.8mm, the difference between the front and back is 0.5mm.