SUBJECT: Operation practices that cause frequent seal and bearing maintenance problems 6-7

Wouldn't it be wonderful if the plant operation and maintenance departments could work independently? The fact of the matter is that there are three types of problems we encounter with centrifugal pumps and poor operation is only one of them. If you're curious, the other two are design problems and poor maintenance practices.

Seals and bearings account for over eighty-five percent (85%) of premature centrifugal pump failure. In the following paragraphs we will be looking at only those operation practices that can, and will cause premature seal and bearing failure. Design and maintenance practices will be discussed in other papers in this series.

When pumps were supplied with jam packing, the soft packing stabilized the shaft to prevent too much deflection. In an effort to save flushing water and to conserve power, many of these same pumps have since been converted to a mechanical seal and the radial stabilization the packing provided has been lost.

The bad operating practices include:

Running the pump dry will cause over-heating and excessive vibration problems that will shorten seal life. Here are some of the common reasons why a pump is run dry:

Dead heading the pump can cause severe shaft deflection as the pump moves off of its best efficiency point (bep.). This translates to excessive heat that will affect both the seal and the bearings as well as causing the seal faces to open, and the possibility of the impeller contacting the volute when the shaft deflects.

Operating off of the best efficiency point (bep.) causes shaft deflection that can fail the mechanical seal and over-load the bearings.

Seal environmental controls are necessary to insure long mechanical seal life. It is important that operations understand their function and need because many times we find the controls installed, but not functioning.

There are some additional things that all operators should know to insure longer rotating equipment life. As an example :

Here are a few common misconceptions that cause friction between maintenance and operation departments

A few more thoughts on the subject

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