SHAFT ALIGNMENT - REVERSE DIAL INDICATOR ALIGNMENT

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SHAFT ALIGNMENT - REVERSE DIAL INDICATOR ALIGNMENT PROCEDURE

• In principle, Reverse Dial Indication (RDI) and Laser Alignment are identical alignment methods each capable of similar accuracy. Below we will cover Reverse Dial Indication method in detail as it explains all the concepts of these two methods in a more understandable graphical sense. If you understand RDI alignment, Laser Alignment method is easy to understand.

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Reverse Dial Indication Alignment:

Step 1:  Refer to section IV for Pre-Alignment considerations 

Step 2:  Determine which piece of equipment is “fixed” and which piece of equipment is “moveable”. In general, you will only be moving one piece of equipment and it is typically, but not limited to, the drive motor.

Step 3: Equipment layout On a piece of graph paper, lay out the piece of equipment being aligned as shown in Fig. 10. The distances needed are: 

1. Distance from where the first indicator rides on the pump hub to where the second indicator rides on the motor hub. In the example shown below, this is 10-1/2 inches.
2. Distance from where the second indicator rides on the motor hub to the center of the front motor feet. In the example shown below, this is 2-1/2 inches. 
3. Distance from the center of the motor front feet to the center of the motor back feet. In the example shown below, this is 5-1/4 inches.

Step 4: Sweep pump hub readings With the indicator bracket attached to the motor hub reading off the rim of the pump hub, zero the indicator on the top and rotate shafts together in 90° increments and take readings.

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Step 5: Correct bottom pump hub reading (Vertical solution) The bottom reading must be corrected for indicator sag, which from section IV we determined this to be negative -.005 inch. To correct the bottom reading you subtract the indicator sag from the bottom indicator reading. The bottom indicator reading was -.025 - (-.005) give us the corrected reading of -.020 as shown in Fig. 11.

Step 6: Plot the first point (vertical solution) The -.020 value is a TIR (Total Indicator Reading) and is two times the actual shaft to shaft distance ( - .020 ÷ 2 = -.010 ). Negative -.010 is the distance between the motor shaft extension centerline and the pump shaft centerline in the plane of the pump hub. A negative sign indicates the dial indicator stem extended at the bottom. With the pump being fixed, the only way this can occur is if the motor shaft is low with respect to the pump shaft. On your graph paper using a scale of small division equal to .001, plot this point as shown in Fig. 12.

Step 7: Reverse the indicator to read the motor hub and sweep readings Now reverse the indicator setup so the bracket is attached to the pump hub and is reading off the rim of the motor hub. As before, zero the indicator on the top and rotate shafts together in 90° increments and take readings.

Step 8: Correct bottom pump hub reading (Vertical solution) The bottom reading must again be corrected for indicator sag. Subtract the negative -.005 indicator sag from the bottom indicator reading of +.005 gives you a corrected bottom reading of +.010. [ +.005 - (- .005) = +.010 ] as shown in Fig. 13

Step 9: Plot the second point (vertical solution) The +.010 value is a TIR number that we divide by 2 to give us +.005, which is the distance between the motor shaft extension centerline and the pump shaft centerline in the plane of the motor hub.

•  A positive sign indicates the dial indicator stem was compressed at the bottom. With the pump being fixed, the only way this can occur is if the motor shaft is low with respect to the pump shaft. Plot this point as shown in Fig. 14.

Step 10: Determine vertical shimming required at front and back motor feet With the pump shaft fixed, these two points represent the location of the motor shaft with respect to the pump shaft. Draw a line thru these two points extending past the plane of the front and back motor feet as seen in Fig. 15. The vertical shim adjustments required to bring the two shafts into alignment can be read directly from the graph. In this example, .004 should be added to the front motor feet and .001 should be added to the back motor feet.

Step 11: Horizontal (side to side) solution Use the same procedure used for the vertical solution only you do not need to correct for sag as the side readings cancel. In the vertical solution you zeroed the top and read the bottom. For the horizontal, you can zero the “near” and read the “far” or vice versa. To zero a reading, simply subtract that reading from both side readings. 

• In our example, the side readings from the motor to the pump in Fig. 11 were negative -.005 (“near” or 9:00 o’clock) and negative -.015 (“far” or 3:00 o’clock). If you choose to zero the near and plot the far readings, subtract negative -.005 from both sides and your “near” reading is now zero and your “far” reading becomes - .010 [-015 - (-.005) = -.010.]

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