17
Preliminary Checks for Alignment of Horizontal Pumps
1.
At least 0.125 inch of nonrusting shims should be installed under each leg of the motor to allow for
adjustments that may be required during the alignment procedure.
2. Compensation should be made for any "soft" or "dead" foot condition. A "soft foot" condition is
comparable to a short leg on a four legged table. To check for a "soft foot," make sure all four feet are
securely bolted to the baseplate. With a dial indicator, check the rise of each foot as its hold-down bolt is
loosened. Retighten the hold-down bolt after the rise is recorded, so that only one bolt is loose at a time. If
one foot rises more than the other three, that foot is the "soft foot." For example, if one foot rises 0.005
inch while the other three rise only 0.002 inch, a 0.003-inch shim should be added to the "soft foot."
comparable to a short leg on a four legged table. To check for a "soft foot," make sure all four feet are
securely bolted to the baseplate. With a dial indicator, check the rise of each foot as its hold-down bolt is
loosened. Retighten the hold-down bolt after the rise is recorded, so that only one bolt is loose at a time. If
one foot rises more than the other three, that foot is the "soft foot." For example, if one foot rises 0.005
inch while the other three rise only 0.002 inch, a 0.003-inch shim should be added to the "soft foot."
3. The hold-down bolt holes should be checked for sufficient clearance to allow for movement during the
alignment procedure.
alignment procedure.
4. Jacking bolts or other fixtures for moving the motor should be fabricated or procured.
5. The mounting brackets and extension bars used for the indicators should be constructed to minimize sag.
Sag is the effect of gravity on the indicator extension bar and can greatly affect the accuracy of the
readings when using the Reverse Indicator Method or rim readings of the Face and Rim Method. The sag
of an indicator bar can be determined by securely attaching the bar to a section of rigid bar stock or a shaft
mandrel. The bar stock or mandrel can be supported and rotated by hand or between centers on a lathe.
With the indicator bar positioned on top, zero the indicator and rotate the bar stock 180 degrees. The
indicator reading will be twice the actual amount of bar sag
Sag is the effect of gravity on the indicator extension bar and can greatly affect the accuracy of the
readings when using the Reverse Indicator Method or rim readings of the Face and Rim Method. The sag
of an indicator bar can be determined by securely attaching the bar to a section of rigid bar stock or a shaft
mandrel. The bar stock or mandrel can be supported and rotated by hand or between centers on a lathe.
With the indicator bar positioned on top, zero the indicator and rotate the bar stock 180 degrees. The
indicator reading will be twice the actual amount of bar sag
sag, add twice the amount of bar sag to the bottom indicator reading. The bar sag is always expressed as a
positive number regardless of indicator convention.
positive number regardless of indicator convention.
Important: The procedures described below for the Face and Rim and the Reverse Indicator
Alignment Methods assume that movement towards the indicator moves the indicator needle in the
positive direction, while movement away from the indicator moves the needle in the negative
direction.
Alignment Methods assume that movement towards the indicator moves the indicator needle in the
positive direction, while movement away from the indicator moves the needle in the negative
direction.
If the indicator used has the opposite sign convention, that is, movement towards the indicator
moves the needle in the negative direction, enter the opposite sign than what is read onto the
worksheet.
moves the needle in the negative direction, enter the opposite sign than what is read onto the
worksheet.
Face and Rim Alignment Method.
The face and rim method of alignment utilizes a dial indicator
attached to one of the coupling flanges to check for angular (dogleg) and parallel (offset) misalignment
untrue surface on the face or rim of the coupling flange, both shafts should be rotated together in the
direction of normal rotation. If it is not possible to rotate both shafts, the indicator base should be attached
to the shaft that is rotated. The procedure is the same whether one or both shafts are rotated. From the dial
indicator readings and the dimensions of the motor, the amount each leg should moved can be
determined analytically. The Face and Rim Worksheet simplifies the required calculations. The following
procedure uses the Face and Rim Worksheet
direction of normal rotation. If it is not possible to rotate both shafts, the indicator base should be attached
to the shaft that is rotated. The procedure is the same whether one or both shafts are rotated. From the dial
indicator readings and the dimensions of the motor, the amount each leg should moved can be
determined analytically. The Face and Rim Worksheet simplifies the required calculations. The following
procedure uses the Face and Rim Worksheet