​Technical Requirements Before Disassembling a Vertical Multistage Pump

From the disassembly diagram of a vertical multistage pump, it’s clear that the pump consists of many parts. It should be disassembled following the correct procedure.

1.Specialized disassembly tools should be used as much as possible.

2.Avoid using excessive force during disassembly to prevent damaging components.

3.For parts that can be easily mixed up, mark their installation orientation or number them after cleaning for organized storage.

4.Review relevant technical documents and previous major/medium repair records. Ask the operators about the pump's recent performance.

5.Cut off the power supply to ensure safety during maintenance.

6.Shut off the pump’s medium supply.

Disassembly Steps for a Vertical Multistage Pump

1. Disconnect the flange bolts on the outlet valve (before the pump) and inlet valve (after the pump) of the multistage centrifugal pump in the pipeline. Separate the pump from the piping. After removing the cooling water pipes, disconnect the coupling between the pump and motor, and remove the coupling from the pump shaft.

2.Loosen the base bolts of the vertical multistage pump. Number the shims at each bolt location in order to ensure they can be reinstalled in their original positions during reassembly. This helps reduce efforts later.

3.Remove the bearing housing: First, take off the connecting bolts of the front and rear bearing housings. Then, slide out the bearing bushings (or bearings) together with the bearing bracket along the axial direction.

4.For shaft seal removal: Unscrew the nuts connecting the gland and the pump casing, slide the gland out axially, and then remove all the packing or pull out the mechanical seal.

5.To disassemble the balancing device: Unscrew the nuts connecting the rear cover and the rear section, remove the rear cover, and then slide out the balancing disc axially. Loosen the screws connecting the balancing ring to the pump casing to remove the balancing ring.

6.Remove the rear section: Take out the balancing disc, balancing ring, etc. Unscrew the through-bolt nuts, pull out the through-bolts, then gently tap the rear section's boss with a hammer until it loosens for removal.

7.Remove the impeller(s): The impeller and pump shaft have a clearance fit but can corrode due to the medium. During disassembly, gently tap around the impeller with a wooden hammer. Once loose, slide it off axially. If an impeller is rusted onto the shaft, soak it in kerosene before removal.

8.For intermediate section removal: Use a pry bar on both sides of the section to loosen it. Once the section is removed, take off the spacing sleeves on the pump shaft between impellers. Remove the suction wear ring and the guide vane/diffuser from the intermediate section. Repeat this process for the remaining impellers and intermediate sections until the suction cover is removed.

9.Remove the long through-bolts: The front section, intermediate sections, and rear section of a vertical multistage pump are clamped together by several long bolts, forming the complete pump body. These are often called "long through-bolts." Proper tightening ensures sealing between sections and prevents medium leakage. Overtightening can damage parts; undertightening causes leaks. Some manufacturers provide a preload value for these bolts in the manual—follow it during reassembly. If no value is given, compare the bolt's length before and after tightening during field maintenance to ensure proper tension.

10.During disassembly, after several intermediate sections are removed, the shaft may become a cantilever. To prevent shaft bending, set up a reliable temporary support. 11.Number and store removed parts like impellers, keys, guide vanes/diffusers, and intermediate sections. After disassembly, clean bearings, the shaft, mechanical seals, etc., with kerosene. Check for damage, excessive wear, or deformation to decide whether repair or replacement is needed. Remove sealing gaskets between sections and clean off any rust.

Post-Disassembly Inspection

1.Clean all removed parts and let them dry. Visually inspect and measure parts; identify and separately store any that are beyond repair.

2.Mark parts that need repair and store them by category.

Disassembly of the Vertical Multistage Pump Motor

1.Based on the site conditions, set up lifting equipment (like wire ropes and tag lines).

2.Check hooks, hoist locks, slings, etc. Test the lifting center of gravity for the motor.

3.Disconnect the motor power cables. Remove the bolts connecting the motor to the pump base and those connecting the motor to the pump coupling.

4.Hoist the motor. Once it is clear of the pump, use the tag lines to lower it slowly. Place the motor on wooden planks, then use a puller to remove the coupling. Take off the fan cover and remove the cooling fan.

5.Record the motor winding insulation. Make alignment marks for reassembly. Unscrew the bolts on the front and rear end covers and remove them.

6.Check the bearing wear. If replacement is needed, use a puller to remove the bearings. The rotor can be pulled out first if necessary. Take care not to damage the stator windings when removing the rotor; use protective measures if needed.

7.For motor bearing replacement, methods like cooling, heating, or pressing with a sleeve can be used.

8.If the bearing outer race is loose, check the fit between the end cover bearing housing and the bearing. If the fit is poor, rework the bearing housing. Reassemble the motor in the reverse order of disassembly.

9.Before final motor assembly, check the winding insulation again. If the windings are damp, dry them out. If necessary, apply insulating varnish with heating. The motor is ready for use if the insulation readings are within the specified range.

Reassembly of the Vertical Multistage Pump

1.After completing rust removal, cleaning, and any repair grinding, reassemble the pump in the reverse order of disassembly. Place the section containing the bearing horizontally on wooden blocks. Mount the discharge section on top. Then, position the shaft through the center of the section with the balancing drum, which has the vertical inlet and outlet.

2.Install the first-stage impeller on the shaft. Place the seal ring/gasket on the outside of the casing.

3.Slide a shaft sleeve onto the shaft, then install the next casing section, followed by the second-stage impeller. Continue installing shaft sleeves and casing sections until all N stages are in place.

4.After the final stage, tighten the two locknuts.

5.Once the above is done, lift the pump body onto the base and tighten the anchor bolts.

6.Install the mechanical seal or packing, then install the bearings and tighten the bearing locknuts.

7.Manually rotate the shaft to ensure it turns freely. Install the coupling.

8.Lift the motor onto the pump. Check the gap between the two coupling halves and align the motor and pump shafts. Tighten the bolts connecting the motor to the pump base.

9.Check that all connection bolts on the vertical multistage pump are tight. Then, reconnect the motor power cables.