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Maintaining Alignment on ANSI Centrifugal Pumps

by PSG

Every operation aims for smooth and optimal performance with their ANSI centrifugal pumps. But occasionally, problems occur in the form of leaks, vibrations or other malfunctions which can cause expensive downtime.

One of the primary causes of pump vibration is misalignment, but this can be controlled by monitoring, and – if necessary – realigning the pump and motor shafts. Here’s how to do it.

Check the Entire Installation First

Before you look at shaft and coupling alignment, you’ll want to inspect the entire pump system for a few key requirements. Specifically, look at the baseplate and make sure that all the mounting bolts are tight and flush. Loose tie down bolts will cause vibration.

Next, look at the piping and make sure it’s aligned with the pump to minimize nozzle loading. You should look at this first, before aligning the couplings. Be sure to conduct the piping – pump alignment checks at normal operating temperature so that you aren’t getting inaccurate readings from thermal expansion.

Align the Pump and Motor Shafts

First, you’ll want to loosen all the bolts on the pump and motor and align the pump with the suction and discharge piping. Once that’s done, re-tighten the piping bolts to set the pump in the correct position on the baseplate.

Next, secure the pump firmly to the baseplate but do not use shims – this will create a soft foot condition, causing vibration that may further misalign the shafts. Make sure the feet on the pump are bolted directly to the baseplate at the correct torque. Once the pump is fastened to the baseplate, you’re ready to align the pump shaft with the motor shaft.

We recommend using a laser alignment tool if you have one, for their accuracy. Not only does this tool provide precise measurements, but it will provide guidance about proper motor repositioning and alignment.

Take Multi-Level Measurements

If you do not have a laser alignment tool, you can use a dial indicator to find the precise shaft alignment.

You’ll need to check both angular and parallel alignment here. This means making sure the motor and pump shafts are at the same height, so one doesn’t angle vertically toward the other – and facing the same direction, so one isn’t too far horizontal of the other.

To check the angular alignment, connect a dial indicator to the pump shaft and the coupling face on the motor end. Mark the coupling where the indicator touches it because you’ll be rotating both shafts together to get an accurate reading. Once the indicator is in place, zero it out, and then rotate it 180 degrees while turning both shafts. The change in reading will tell you xhow far out of angular alignment the shafts are.

NOTE: To measure for the horizontal alignment, position the indicator at 3 and 9 o’clock. If you place the indicator at 12 and 6 o’clock, you’re measuring the vertical alignment.

For parallel alignment, the procedure is similar. Place a dial indicator on the outer rim of the motor shaft coupling. Then set the indicator to zero and rotate both shafts 180 degrees. Check the change in the reading against the tolerance specs and adjust as needed until your measurements are within the required range.

The correct pump alignment is a critical factor in eliminating pump vibration which can lead to other problems and even total pump failure. With these steps, you should be able to ensure both the pump and motor shafts are aligned and allowing your pumps to operate smoothly.