Slurry Pump Impellar Removal and Adjustment Guidelines
With a Gland Seal assembly fitted, both Rubber and Metal Lined Slurry Pumps should be adjusted to operate with the Impeller having minimum axial clearance with the front casing liner (Throatbush or Cover Plate Liner). This is most important with High Efficiency Impellers. Adjustment of Impeller front-end clearance is carried out as follows:
a. Rotate the Shaft clockwise (as viewed from the drive end) by hand, and move the Bearing Assembly forward (towards the pump intake) by adjusting the rear nut on the ADJUSTING SCREW until the Impeller rubs on the front Liner.
b. Unscrew the rear nut by one sixth of a turn, and move the Bearing
Assembly back by adjustment of the front nut on the Adjusting Screw until the plug on the Bearing Assembly contacts the rear nut. Fully tighten the front nut to secure the Bearing Assembly in position.
c. Ensure that the Shaft can now rotate freely without contact of the Impeller with the front Liner. If contact occurs, repeat step (b).
NOTE: After each Impeller adjustment is completed, the BEARING HOUSING CLAMP BOLTS must be tightened to torque values indicated in (Ref.2), below. If a torque wrench, or equivalent device is not available, bolts should be tightened as Ref.3.
With a Centrifugal Seal or Super Seal assembly fitted, the pump should be adjusted to operate with the Impeller having approximately equal axial clearance with the front and rear casing liners.
If leakage occurs from the Centrifugal or Super Seal during slurry pump operation, the Impeller should be adjusted rearwards to minimize axial clearance between the Impeller and rear casing liner.
If seal leakage persists after Impeller adjustment, this indicates that the intake pressure is excessive for the Impeller fitted. Leakage may be prevented by fitting of an alternative Impeller having improved intake pressure sealing characteristics. This may require fitting of a differential Impeller.
Periodic adjustment of Impeller clearance over its operating life is an important factor in maximizing wear life of both Impeller and front Liner. Extensive field experience has shown that an increase in wear life of up to 50 percent can be achieved by regular Impeller adjustment, compared with pumps not subject to initial or ongoing adjustment. Regular Impeller adjustment has shown an increase in wear life of typically 20 percent compared with pumps subjected only to initial adjustment.
a. At initial pump assembly, adjust Impeller to “just clear” the Throatbush or front Liner, as described in (1).
b. After 50 to 100 hours of slurry pump operation, re-adjust Impeller front-end clearance.
c. Re-adjust Impeller front-end clearance a further two or three times at regular intervals over its wear life. This may coincide with regular pump maintenance intervals, typically 500 hours.
NOTE: After each Impeller adjustment is completed, the BEARING HOUSING CLAMP BOLTS must be tightened to torque values indicated in (Ref.2), below. If a torque wrench, or equivalent device is not available, bolts should be tightened as Ref.3
For CLAMP BOLTS on the bearing housing
Removing the slurry pump impeller from a slurry pump for routine maintenance can usually be accomplished by securing the impeller against rotation and applying reverse torque to the shaft through a spanner or lever attached to the overhead crane. A few sharp hits with a hammer will generally loosen the plug threads if they have been properly coated with anti-seize and two release gaskets were used.
As the wear life of TOWER wet end parts continues improving, the corresponding maintenance interval increases. Longer life and harsh duty conditions can result in the impeller to lock tighter on the shaft over time and make routine removal difficult.
Under no circumstances should heat be applied to the impeller! Air and moisture trapped in the internal cavity can expand and cause the impeller to explode!
Never operate the motor backwards to loosen or remove the impeller! This can result in mechanical damage and possible injury to personnel. Under the condition, when normal maintenance procedures could not remove the impeller, a technique using a drop bar and the impeller inertia can be used to break the threads loose lightly. The end of a weighted bar is lifted and allowed to drop, turning the impeller in the normal operational direction. When the end of the bar hits a stop plate on the floor, the shock of the sudden stop combined with the inertia of the impeller will generally loosen the plug threads.
Mild steel should be used. Fabricate a plate that bolts to the coupling half or sheave on the pump shaft. This can be made to attach in the gap between the coupling sections. Multiple bolt patterns will accommodate different pumps in the facility. Using a length of beam, plate or steel tubing, add the longest practical arm that will safely rotate from near vertical to the floor or other solid stop point. On the end of the arm add a weight which doubles as an impact face. For most slurry pumps, use about 180kg or a block about 600 x 255 x 150mm. A ring or other release point is installed on top. Be certain that all parts are welded adequately as the impact forces can be severe. If plate is used for the arm, it should have a brace or gussets to prevent bending.
Use proper safety practices and keep all persons away here. Place a steel plate on the impact area of the floor to avoid any other damage. Verify that the arm will rotate the impeller in the correct direction. Raise the arm with the overhead crane to a near vertical position and release it.
Allow the arm to drop and hit the plate. It may take multiple hits. Once the slurry pump impeller is free to turn on the threads, install the impeller lifting device and complete the removal procedure.