There are many outside influences that affect a precision shaft alignment. One that seems to be overlooked is pipe hanger location and condition.
The weight of the piping on the pump, when pipe hangers are missing or incorrectly spaced, can cause deformation of the pump housing and the base, essentially putting a strain on all the components. When a process pipe is in operation and the line is full, there can be a great deal of weight change from when the piping is empty while doing an alignment.
Here is an example of how the unsupported discharge piping of a 7.5HP electric motor and overhung centrifugal pump changed the alignment when the piping was connected.
Alignment with pipes disconnected
Changes to alignment after full pipes with missing hangers were connected
Obviously, the larger the pipe diameter and consistency of the process fluids will vary this effect tremendously. If the piping is properly supported, the influences can be eliminated completely. There are piping manufacturer recommendations as to the proper location and distance between hangers.
As a rule of thumb when cast iron is used for pressure the distance between hangers should not exceed 12 feet. When cast iron is used for soil pipe, the recommendation is 10 foot maximum spacing. According to ITP’s Pipe Trades Manual, hanger locations for steel pipe systems varies based on size. This range is from 7 feet apart for 1 ¼” diameter piping to as far 33 feet apart for 24” diameter piping.
Regardless of the size, it is a good practice to walk your piping systems to locate potential influences caused by broken, loose, missing or incorrectly spaced pipe hangers.