SHAFT ALIGNMENT PROCEDURE

SHAFT ALIGNMENT - REVERSE DIAL 

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.

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.

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.]

• SHAFT ALIGNMENT - FLEX ELEMENT ALIGNMENT

  SHAFT ALIGNMENT - FLEX ELEMENT ALIGNMENT PROCEDURE
  
  
  

  

  • When the distance between coupling flex elements is long, making use of indicator brackets impractical or where lasers cannot be targeted due to obstructions or beam interference, Across the Flex Element Alignment method can be used. 

  In this method, angular and axial misalignment will be checked as described below respectively:

  
  

  Angular alignment:

  
  

  Step 1: Squarely and firmly attach a dial indicator to the center member shaft and read across the flex element to the driver hub surface facing away from the indicator mounting as seen in Fig. 16.

  

  
  

  Step 2: With the dial indicator set to zero, rotate the shaft one revolution and record the maximum and minimum dial indicator readings. 

  
  

  Step 3: If the range between the maximum and minimum reading is at or below .010 inch, the angular alignment is acceptable. If the range is greater than .010 inch, the equipment should be realigned. 

  
  

  Step 4: Repeat steps 1-4 on the driven side flex element.

  
  

  Axial Alignment:

  • To establish the axial misalignment, you will measure the gap between the spacer flange and connected equipment hubs, on both flex points of the coupling, and compare with published coupling limits. 

  Step 1: Without rotating the coupling, take four gap readings at 3:00, 6:00, 9:00 and 12:00 o’clock between the driver and center member flanges as seen in Fig. 17.

  
  

  

  
  

  
  

  Step 2: Average these four readings. 

  
  

  Step 3: Consult the coupling installation instructions for the coupling size and style being installed to be sure the average reading are within acceptable axial installation limits. If the coupling being aligned is an Addax® coupling, the nominal gap for all sizes is .540 inches and should be between .530 and .550 inches. 

  
  

  Step 4: Repeat steps 1-3 on the driven side flex element.

ALIGNMENT - LASER ALIGNMENT METHOD

 ALIGNMENT - LASER ALIGNMENT METHOD

• The laser alignment method is considered a precision-based performance technique that provides a faster, more accurate way to align equipment.

• It is ideal for alignment of equipment over long distances, and it is less prone for user error. Because of the range of technology between various manufacturers, the steps for laser alignment are not discussed in detail in this article.

PROCEDURE:

• laser alignment system installed on a pump and electric motor. The system contains a laser diode and position sensor on one mounting bracket.

• The diode emits a pulsating, non-hazardous, laser beam that is directed at the opposite bracket. The opposite bracket contains a prism that redirects the laser beam back to the position sensor. Like other shaft alignment techniques, the shafts are rotated to determine the vertical and horizontal readings for angular and parallel misalignment.

• The shaft positions and readings are automatically provided to a small computer. The computer then calculates the relative movement required at the feet of the moveable machine.

• A major advantage of the use of laser alignment is the precise measurement of misalignment. Laser alignment can detect misalignment to ±0.00004”. In addition, with the use of laser alignment, bar sag concerns are eliminated.

• However, there are drawbacks and limitations to the laser alignment method. Laser alignment equipment typically costs more than $10,000. Service companies or those companies with many pumps or large pumps are the primary buyers of laser alignment equipment.

• The environment in which the laser alignment equipment is used is also a limitation. The atmospheric temperature must be between 32° and 131° Fahrenheit for the use of laser alignment. The environment must also be free of steam, dust, or air currents.

• These detractors will prevent the reading of the laser beam properly. However, it is possible to use a plastic pipe to shield the beam from the steam, dust, or air currents.

FINAL CHECKS AND WORK CLOSEOUT :

After the equipment has been aligned, some additional tasks and checks should be performed.

• Make sure that each shaft turns freely with the coupling hubs installed.

• The safety equipment should be removed and the equipment energized

• The driver should be “bumped” to check for proper rotation.

• Reinstall the safety precautions and complete the assembly of the coupling per the installation instructions.

• Rotate the coupled shafts to ensure they turn freely.

• Install the coupling guards per OSHA or applicable requirements.

• The safety equipment should be removed and the equipment energized.

• Once the pump is ready to operate, the pump and piping that has been drained should be filled. As the pump and the system piping is filled, observe for any piping distortion due to improperly supported piping. Poorly supported piping may cause misalignment.

• After the piping is installed, the pump unit is operated under normal conditions and is thoroughly warm, stop the pump unit to recheck alignment while it is warm. This also ensures that there is no additional pipe strain.

• If additional alignment is required of more than 0.002” from the pipe free condition, the additional piping strain should be corrected. Additional discussion on piping installation can be found in another article.

• For high energy and petroleum pumps, the pump and driver feet are drilled and doweled at two locations, near the thrust bearing end, after the final alignment is complete and meets the specifications.

• Documentation of the alignment is important to the installation and operation of the equipment. Make a record of the final alignment tolerance on an alignment form or data sheet. This should be placed in the equipment’s history file. This provides not only proof of final condition, but allows a starting point and historical data for the future.

• For work done in the future, this information will allow for the alignment to be done quicker and smoother, saving set up time. In will also provide a basis to allow for measurement of operational time.

• Reporting or recording sheets can be developed to include information on soft feet, pipe stress and strain, coupling and shaft runouts, installation conditions such as bolts being found loose, and specifying the initial, desired, and final alignment information.

• The sheet should also provide a location for identification of the persons completing the work to be documented. This places responsibility of quality work on individuals, and provides learning opportunities if a failure occurs.

• Reported data allows for troubleshooting and root cause analysis of equipment failures. The data can be used to compare the “as discovered” condition and the “as completed” condition. This can be particularly useful for equipment with chronic abnormal behavior.

• Another useful tool for recording data are digital photos. Pictures of the shaft, coupling, base, and foundation conditions can be stored. These could be used in the future during set up to determine any special needs or how the installation was left.

• Although alignment should not be scheduled to be rechecked with the frequency of preventative maintenance procedures, it should be rechecked when observations are made in regards to the settling of the base, foundation, or soils, changing of the piping system, process changes, or seasonal temperature changes.

• For a new installation, the alignment should be scheduled to be rechecked 3-6 months after the initial installation and alignment.