10 Steps for Proper Pump-Pipe Alignment


Written by:
Lev Nelik, P.E., Pumping Machinery, LLC
Published:
June 19, 2012

Once rough alignment has been completed, remove the equipment (pump, motor gearbox) from the baseplate. Level the baseplate to a maximum out of level of 0.025 inch (0.06 millimeter) from end to end in two planes. Use machined pads as the base for the leveling instruments. Inspect the foundation for cleanliness, and if not clean, use a solvent to remove grease and oil.

Figure 3. Baseplate leveling pads and grout location

 

Step 4

 

Allow time for the cleaning substances to evaporate. Form the base using the appropriate techniques to allow for the weight, temperature rise and fluidity of the grout material. Use epoxy grout to secure the base, and allow the grout to cure, following the grout manufacturer’s recommendations. This normally requires 24 hours at 80 F (27 C). Remove the forms and clean all sharp residue and edges from the foundation.

Figure 4. Typical anchor bolt and leveling wedges

Step 5

 

The rough alignment step, mentioned above, is critical to minimize the changes that will be required to appropriately fit the piping to the pump. At the last stage, when the final spools are installed, the final alignment will be achieved with small adjustments. This will minimize the adjustments required on the motor feet/bolts. Unfortunately, motor hold-down bolts are often too tight and allow for only small adjustments to the motor before becoming bolt bound.

Motor manufacturers could improve this situation significantly if motor feet were slotted by design rather than drilled for bolts. Figure 5 shows the tightness of space available to insert the foot hold-down bolt. This illustrates once again why good alignment at Step 3 can save time and the cost of having to alter motor feet (which can be a nightmare) by slotting or reaming.

Figure 5. Potential bolt-bound situation due to tight clearances between bolt, feet and base

 

Step 6

 

Reinstall the pump and the motor on the baseplate. Rough align the equipment again, using a reverse indicator, laser alignment or similarly accurate technique. It should now be easy to fine-tune the motor movement within the allowable alignment target without becoming bolt bound. This is possible because of completion of the rough alignment during Step 4. Note: Never install shims under the pump feet. If the shims are lost or misplaced then alteration to the piping may be required to get the pump within the required alignment specification. The normal procedure is to place 0.125-inch (3.2-millimeter) thick shims under the motor feet. This allows for adjustments that will be required during final alignment.

 

Step 7

 

Make up the final spool pieces for the suction and discharge spaces. Bring the piping to the pump now.

 

Step 8

 

As a final alignment step, bring the piping to the equipment. Take final measurements, and tack weld the spools in place. At this time, the spools can be removed and taken back to the hot work permit area to finalize the weld. Leave a square and parallel gap between the flange faces. The gap should be wide enough to accommodate the size of the gasket required, plus 1/16  to 1/8 inch, depending on the piping sizing. This is the only distance through which the piping will be pulled. However, because it is properly anchored before the spool pieces, this length is short, and stresses are minimized. Finally, align the equipment, considering hot and cold operating conditions, using two indicators on the pump shaft coupling area.

 

Step 9

 

As the piping is tightened into place, the shaft must not be moved more than 0.002 inch (0.005 millimeter). Otherwise, modify the spool pieces until the piping misalignment is fixed. Several conditions are common when piping is misaligned. Some of these conditions are the mechanical seal and/or the bearings running hot and other component failures. A quick analysis of the failed parts will clearly show the signs of piping misalignment. To make a final confirmation of the symptoms, unbolt the piping while measuring the movement in the vertical and horizontal plane. Again, piping that moves more than 0.002 inch (0.005 millimeter) must be modified to correct the situation.

 

Step 10

 

Place an indicator in the horizontal and vertical planes, using the motor and pump coupling.

Uncouple the pump and motor, while watching the indicators for movement. Start unbolting the flanges, and continue watching for movement in the indicators. If the needle jumps more than 0.002 inch (0.005 millimeter) the piping has to be modified to improve the pump’s performance.

 

References

 

1. AlChE Equipment Testing Procedure for Centrifugal Pumps (Newtonian Liquids), 2nd Edition, AlChE, New York, 1984.

2. AlChE Equipment Testing Procedure for Rotary Positive Displacement Pumps (Newtonian Liquids), Second printing, New York, N.Y., 1968.

3. AlChE Equipment Testing Procedure, New York, N.Y., 1999.

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See also:

Upstream Pumping Solutions

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