Home .Empowering Pumps Alignment Challenges on Small Positive Displacement Pumps

Alignment Challenges on Small Positive Displacement Pumps

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Stan Riddle

Contributor: Stan Riddle, VibrAlign-ACOEM Group

Positive displacement pumps, like the one in this photo, are common in industry.  This one uses a small horsepower motor, attached via a C-face mount to a gearbox, which drives the pump.  

Even thought this type of machine often has a fairly slow output speed, proper alignment of the gearbox to the pump will reduce vibration and increase component life.

A few things to keep in mind:

  • The motors are often unsupported underneath, but use the C-face flange to hold the motor in place.  When the gearbox hold down bolts are loosened (as when performing precision alignment) the motor will drop, and lift the output side of the gearbox.  This weight MUST be supported. A machinist’s jack, pipe support, or other method should be used to support the weight of the motor.


On this pump, the packager has included a steel strap underneath the motor, with a jacking bolt and jam nut.  This is not meant for alignment, but to simply support the motor, in case it is bumped, stepped on, or otherwise pushed downward.  Alignment should be completed by positioning the gearbox. Once the alignment is completed, the bolt should be run down until it touches the steel plate, and locked with the jam nut.

  • Jacking bolts should be used to move the gearbox horizontally.  If they are not installed on the skid, it is easy to either tack-weld nuts for jacking bolts, or employ some other methods, such as bar clamps, to move the gearbox horizontally.  Hammers should not be used to move the motor and gearbox assembly.
  • The skids on these types of pumps are somewhat flexible.  Precision alignment should be done:
    1. When the pump assembly is built, or when it is first received by the user.
    2. Again once the pump is set into place.
    3. And again, once all piping and conduit is attached.  If the pumps is moved, it should be re-aligned.

Proper alignment of the coupling, even on slow-speed machines, will increase the life of the pump and gearbox.

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