Soft foot

Soft foot is a condition where the pump feet are not in proper contact with their
mounting pads, or pedestals, on the baseplate - they are not on the same plane. It
is analogous to leaning on a table and finding that the table tilts because not all of
its feet are flat with the floor.

Checking for soft foot

There are two slightly different methods in checking for soft foot but their basic
principle is the same:

  • Set the pump on its baseplate and place a dial indicator on one foot.
    Tighten the hold down bolt slowly and watch the dial indicator. If the pointer
    moved by [ * ] while tightening the bolt the pump has soft foot.

  • Or, set the pump on its baseplate and bolt it down. Place a dial indicator
    on one foot, loosen its hold down bolt slowly, and watch the dial indicator.
    If the pointer moved by [ * ] while loosening the bolt the pump has soft foot.

The amount of movement measured by the instrument indicates how much shim
is needed underneath to level the pump. Repeat this procedure on each of the
pump foot.

Soft foot should be corrected by shimming. Never try to correct it by over-tightening
the bolts - it will induce harmful stress on the casing that can result in permanent
casing distortion, or deformation, if left uncorrected for some time.

Both pump and its driver should be checked for soft foot.

[ * ] Some information are excluded in this article.
Read more.

Category: installation, trouble-shooting
File: baseplate soft foot

"Make it simple"
Photo shows a typical API 610 pump baseplate. It should be checked for soft foot during pump installation.

Which of the two methods mentioned above by CENTRIFUGAL-PUMP.ORG is
preferable, and why?

Consider a situation where a pump has been shimmed and aligned. If the bolts
are loosened one at a time and the shims spring back such as to open a gap in
the four feet, say, to 0.10, 0.12, 0.10, and 0.18, should all four feet be considered
as "soft foot", or only the one with 0.18 (treating the 0.10 as the reference point,
this being the lowest value)?

Related topic: Designing steel-reinforced concrete foundation





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