How to Align a Pump
Misalignment is the leading cause of premature pump bearing and seal failure. Learn the rim-and-face dial indicator method for precise shaft alignment.
Why Alignment Matters
Pump-motor misalignment causes vibration, overheating, premature bearing failure, mechanical seal damage, and coupling wear. Even a small angular or parallel offset can reduce bearing life by 50% or more.
Proper alignment extends bearing life, reduces energy consumption, and eliminates the most common cause of unplanned pump failure.
Two types of misalignment
Angular misalignment: the shafts are at an angle to each other (not concentric). Parallel (offset) misalignment: the shafts are parallel but offset. Most real misalignment is a combination of both.
Tools Needed
- Dial indicators: Two dial indicators with magnetic bases, or a laser alignment tool.
- Shims: Stainless steel shims in various thicknesses (0.05mm, 0.1mm, 0.2mm, 0.5mm, 1.0mm).
- Spanners: Correct size for motor holding-down bolts.
- Feeler gauges: For rough alignment before dial indicators.
- Dial caliper: For measuring shaft diameters and coupling hub dimensions.
Step 1: Preparation
- Lock out and tag out the motor — ensure it cannot be started during alignment.
- Remove the coupling guard and separate the coupling halves or loosen the coupling spacer.
- Clean the coupling hubs, shaft ends, and shimming surfaces.
- Check for soft foot: use a dial indicator on each motor foot, and loosen each bolt one at a time. If the indicator moves more than 0.05mm when a bolt is loosened, the motor has soft foot and must be shimmed before alignment.
- Roughly align the shafts using a straight edge across the coupling hubs.
Fix soft foot first
Soft foot (where one motor foot doesn't sit flat on the base) makes accurate alignment impossible. Fix it first by shimming the raised foot before proceeding with dial indicator alignment.
Step 2: Rim and Face Alignment Method
The rim-and-face method uses two dial indicators: one measures the radial (rim) offset, the other measures the angular (face) offset. Both are mounted on one shaft and read against the other.
- Mount the rim indicator on the pump shaft (or coupling hub), with the plunger reading the outer rim of the motor coupling hub.
- Mount the face indicator on the pump shaft, with the plunger reading the face of the motor coupling hub.
- Set both indicators to zero at the 12 o'clock position.
- Rotate both shafts together 180° to the 6 o'clock position. Record both readings.
- The rim reading gives the parallel (offset) misalignment. The face reading gives the angular misalignment.
- Rotate to 3 o'clock and 9 o'clock to check for lateral misalignment.
| Reading at 6 o'clock | What it means |
|---|---|
| Rim = 0, Face = 0 | Perfectly aligned (unlikely on first try) |
| Rim ≠ 0, Face = 0 | Parallel offset only — shim the motor feet equally |
| Rim = 0, Face ≠ 0 | Angular misalignment only — shim front and rear feet differently |
| Rim ≠ 0, Face ≠ 0 | Both angular and parallel — correct both |
Step 3: Correct the Angular Misalignment
Angular misalignment means the motor shaft is at an angle to the pump shaft. Correct it by shimming the front or rear motor feet differently.
- Measure the distance between the coupling face and the motor front foot (A).
- Measure the distance between the motor front foot and rear foot (B).
- Calculate the shim correction for the rear feet: shim thickness = (face reading ÷ coupling diameter) × (A + B).
- Add or remove shims at the rear feet as calculated.
- Re-measure and adjust until the face reading is within tolerance.
Tip: Use the formula: shim correction at rear = (face reading ÷ coupling diameter) × distance from coupling to rear foot. Positive means add shims; negative means remove.
Step 4: Correct the Parallel (Offset) Misalignment
Once the angular misalignment is corrected, address the vertical offset. The rim reading shows how much the motor needs to be raised or lowered equally at all feet.
- The rim reading at 6 o'clock shows twice the actual offset (because the dial rotates 180°). Divide the rim reading by 2 to get the actual offset.
- If the rim reads positive, the motor is too low — add shims equally at all four feet.
- If the rim reads negative, the motor is too high — remove shims equally at all four feet.
- Re-check the face reading — correcting parallel may slightly affect angular.
- Repeat the angular and parallel corrections until both are within tolerance.
Step 5: Lateral Alignment
Once vertical alignment is correct, check lateral (horizontal) alignment. Rotate the indicators to 3 o'clock (zero) and then to 9 o'clock. The readings show lateral angular and offset misalignment.
- Correct lateral angular by moving the motor sideways at the rear feet.
- Correct lateral offset by moving the motor equally at all feet.
- Use the motor holding-down bolts and jack screws (if fitted) for fine adjustment.
- Re-check all four readings (rim and face at 6 and 9 o'clock) until within tolerance.
Alignment Tolerances
| Speed (RPM) | Max angular (per 100mm) | Max parallel offset |
|---|---|---|
| Up to 1800 | 0.05 mm | 0.08 mm |
| 1800–3600 | 0.03 mm | 0.05 mm |
| 3600–6000 | 0.02 mm | 0.03 mm |
| Above 6000 | 0.01 mm | 0.02 mm |
Thermal growth
Electric motors heat up and grow vertically during operation. For a typical 15 kW motor, thermal growth can be 0.05–0.10 mm. Consult the motor manufacturer's thermal growth data and pre-offset the motor by that amount when cold, so it grows into alignment at operating temperature.
Final Steps
- Tighten all motor holding-down bolts in a crisscross pattern.
- Re-check the alignment — tightening bolts can shift the motor.
- Reconnect the coupling and reinstall the coupling guard.
- Remove LOTO and run the pump. Check for vibration at the coupling — if excessive, re-check alignment at operating temperature.
- Log the final alignment readings in the maintenance record.