Measurement of shaft run out is not very difficult with a run out gauge. The gauge consists of a probe that extends from the gauge dial. A needle on the dial indicates the amount of deflection caused by rotation of the mixer shaft. Run out will indicate any static misalignment or bending of the shaft. The gauge is mounted, often to a magnetic or clamp mount, so that the gauge can be held stationary while the probe rests against the shaft. See the accompanying picture:

 

The shaft is then rotated slowly, typically by hand, and the gauge shows the changes in the shaft location relative to flange or other support.

To measure shaft run out at the location of the seal, the seal should be removed from the shaft, the drive or support installed, and the shaft rotated slowly while in contact with the run out gauge. The run out should be less than 0.010 inch at the seal location. Higher values will increase wear on the seal.

Static run out will tell a significant part of the story. If you cannot get small run out values while slowly rotating the shaft, the run out will only increase with the mixer under load. If the run out gauge can be safely mounted against an exposed portion of the mixer shaft near the seal location, it may be possible to make run out observations with the mixer running. Running the mixer under load, as with a tank full of water will only add to the observations.

Any and all measurements should be made under carefully controlled and safe conditions. Installation of a run out gauge and manual rotation of the shaft should only be done with full lock-out and tag-out safety. Operation of the mixer should only be done after the gauge is installed with lock-out and tag-out conditions. Removal of any safety guards to observe run out should be done extremely carefully, with personnel as far as possible from rotating parts. Immediately following measurements, the gauge should be removed and guards replaced. SAFETY FIRST. Solving a seal leak problem should never involve injury to personnel.