Pump Troubleshooting
One of the major problems facing industry today is the limited number of people who have sufficient
skill and experience to diagnose and rectify the basic problems plaguing centrifugal pumps. The other
major difficulty is that the same lack of skill and experience is creating many of these problems in
the first place.
A detailed evaluation of a pump problem requires a depth of knowledge, which usually surpasses that to
which most people are ever exposed. For example, most pump engineers, operators and maintenance people
develop their knowledge base from the same “school of hard knocks.” While many aspects of on-the-job
type of training are commendable, it unfortunately exposes the pupil to the opportunity of learning
other people’s mistakes and misconceptions. At best, it only teaches what is necessary to execute a
particular job function in exactly the same manner as it was previously performed—good or bad!
A system engineer may have learned how to size a pump based on the operating parameters of the system.
However, if that pump is unable to withstand the effects of certain installation or operating anomalies,
which may occur in that plant, the reliable life of the pump could be detrimentally affected.
A purchasing manager may be faced with the responsibility of buying equipment within a capital cost
budget that has no mechanism for the evaluation of long-term operation and maintenance costs.
Consequently, the “most economical” pump purchased may result in frequent and repetitive failures that
could quickly exceed the initial cost difference and even the total price of the pump itself.
Operations personnel are often required to “tune” the system to provide the desired output of product.
As a consequence, they may be faced with the necessity of throttling back the pump discharge valve, and
that can result in a variety of hydraulic and mechanical problems in the pump.
The ramifications of all such situations are generally imposed on the maintenance department.
Regrettably, the training in that group has traditionally been limited to the physical change-out of
the parts when a breakdown occurs. As the underlying cause of pump failure often extends well beyond
the failed item, these maintenance methods will effectively reinstall the same old problem. This is
particularly disturbing when we realize that over 80 percent of all pump failures tend to manifest
themselves at the mechanical seal or the bearings, which then act in a manner similar to a fuse in an
electrical system—they fail.
Just because a fuse fails, doesn’t mean there is anything wrong with the fuse! In fact, the problem is
almost always somewhere else in the system. The same frequently holds true for seals and bearings. In
spite of this, when these components fail, we rarely look for the real problem. Instead, we simply
replace the offending part. While that will occasionally solve the problem, the simple change-out of a
seal or bearing rarely provides long-lasting relief from the problem.
So Let’s Get Practical! Let’s consider the two different types of pump problems—those that are either
operational or reliability in nature—as well as some sources of these problems and some tools for
identifying their underlying causes.
Failure Analysis
As there are only a few symptoms with which to recognize a troubled pump, the key to failure analysis
lies in understanding how the combinations of symptoms identify the underlying cause of the problem.
An effective troubleshooting tool will always begin with the question, “How fast did it show up?” If
the problem has only suddenly appeared, it is likely to have a different cause than a similar problem
that has slowly been developing over time. It is also fairly obvious that a sudden appearance of the
problem is probably caused by a sudden change in the condition creating the problem. Therefore, it is
highly unlikely that such a problem can be attributed to normal wear and tear. It is much more probable
that an inappropriate action has taken place recently.
The exception to the foregoing concept is where wear gradually takes place until the point at which
failure suddenly occurs. In such an event, however, the wear is usually indicated by a gradual
reduction in performance until the breaking point is reached, thus providing some prior notification of
imminent failure.
Operational Problems
This is the type of problem where the pump simply doesn’t produce the hydraulic results for which it
was intended. A typical example of this occurs when the centrifugal pump isn’t pumping enough liquid
through the system. While this is often blamed on an inadequate pump, it is more often the fault of a
higher-than-expected system head.
Troubleshooting a low flow condition
Another example is when the pump is operated so far away from its design point that it begins to
vibrate as a result of a variety of hydraulic conditions.
Reliability Problems
Reliability problems bring into question the length of time the pump can be expected to continue
running. A typical example is when a pump is vibrating as a result of a variety of mechanical
conditions.
Although there have been almost 100 different problems associated with centrifugal pumps, many of which
have more than one solution—sometimes they have two, three or even more solutions—it’s interesting to
note that the total number of solutions for these 100 different problems is less than 40. In fact, if
you scrutinize the accompanying tables, it is evident that there really are only six basic solutions to
pump problems.
They can be summed up as follows:
- better sealing devices
- component modification
- system change
- new pump
- personnel training
Of these six solutions, the one that will have the most significant and far-reaching effect (as well as
be the most practical one) will continue to be that of providing adequate personnel training. This
means that everyone who has anything to do with the sizing, selection, installation, operation and/or
maintenance of the pump is fully skilled and experienced in their own particular function, as well as
aware of how their actions impact the reliability of the pumping system.
Innovative Process Solutions, When Performance Counts.