SUBJECT : A technique for
making troubleshooting decisions 7-7
The rules are very simple. Decisions have to be
made when doing nothing will cause the condition to degenerate.
As an example: if you can live with the present
leak rate, you don't have to make any decisions about fixing the
leak, but If you can't live with the problem because the pollution
people are going to close you down, then you better start making a
decision and the following sequence should help you come up with the
- Decide if this is a generic problem, or just a
- Decide what the decision really has to
- Be prepared to do what is right rather than
what is convenient or acceptable.
- Know that nothing is going to happen until the
decision is converted to action.
- You are going to need a feed back system to
compare the results of your decision or action. In other words you
have to test the results.
Let's look at each of these points in
1. Generic problems require a specification,
standard, rule, policy or principle. It is only then that
manifestations of the same generic situation can be handled
intelligently. There are four possibilities you will
- The problem is truly generic. The individual
occurrence is only a symptom of a much larger problem.
- Example: The seal is failing because of
shaft deflection caused by starting the pump with the discharge
valve shut in an attempt to save power. The shaft has to be
stabilized or this problem will reoccur each time the equipment
- It is a unique event for the individual, but
actually is a generic problem.
- Example: The ceramic face fractures in hot
water, but seems to work well in other fluids, or the carbon
face pits in higher temperature hydrocarbons but has no problem
in other hot fluids. Problems of this type are only solved by
educating the work force or having only qualified people do the
- It is truly exceptional, a really unique
- Example: The seal leaked when the pump was
at operating temperature, but does not leak at start up or
during shut down because the carbon was pressed into a metal
holder and became loose due to the differential expansion rate
of the metal holder and the carbon. It did not have enough
squeeze or interference. This is a quality control
- You are seeing the early manifestation of a
new generic event.
- Example: The carbon cracked when the O-ring
on the Inside diameter of the seal face swelled up due to
chemical attack. It happened when your plant instituted a new
line cleaning process that uses a chemical that is not
compatible with the elastomer.
It would be foolish to treat any new event as just
another example of an old problem. Blaming operator error and bad
maintenance practices is frequently used to mask generic design
problems. The fact is that most pumps and mixers in use today were
never designed to be used with mechanical seals. The long, overhung
shafts were designed to be supported by multiple rings of lubricated
packing. The result of this design error is that premature seal and
bearing failure has become the norm. The truly generic problem is
being treated as a "unique event". Shaft/sleeve fretting, water in
the bearing oil, and oil seal shaft damage are actually generic in
nature, but seldom addressed as such. It is far easier to blame the
problem on dirt in the atmosphere or in the product and then replace
the hardware to have the experience repeat its self over and over
The hardest thing to realize its that there are no
"facts" for you to act on. There only events until someone makes them
relevant. You must decide if the explanation explains the observed
events and if it explains all of them.
2. Now that you have decided you have a generic
problem, and a decision to correct the problem has been made, can you
verbalize what the decision has to accomplish? Here are a few
examples of what is possible:
- Standardizing on good seal materials can avoid
common material mix up problems. Do not leave material decision
problems to the vendor. He is oriented to choose the lowest cost
material that will perform the function properly. He has not been
trained to think in terms of solving spare part and material mix
- Balanced o-ring
seals can function in both pressure and
- O-rings are the only elastomer shape that can
seal in both directions.
- Balanced designs balance the opening and
closing forces acting on the seal faces to prevent leakage and the
generation of destructive high heat.
- Two way balance
is necessary in dual seal applications
so that you can choose either a high or low barrier fluid pressure
between the seals and not be concerned about the seal faces
blowing open when and if the pressures reverse.
- A low L3/D4
pump shaft will resist excessive
shaft deflection and movement. This is an important consideration
if you want to increase seal and bearing life.
- A stuffing box heating jacket can be
controlled to prevent many chemicals ( caustic, sugar, etc.) from
crystallizing, vaporizing, solidifying etc.
- Centerline design pumps can eliminate a lot of
misalignment problems and wear ring damage when the pumping fluid
temperature exceeds 200°F (100°C)
- The correct grade of carbon/graphite can run
dry for long periods of time.
3. Now we come to the third and hardest part of
the process, Are you prepared to do what is right rather than
acceptable or convenient? Insight is not achievement. You will be
judged on your results not your words. No matter how many people are
involved, the results will always be identified with a single name
and it probably will be yours.
Unfortunately a change in supplier, design, or
specification makes some one look like he made a wrong initial
decision. Too often companies keep doing the same old thing because
the boss will "lose face" or it is too difficult to change the
Change is always difficult and uncomfortable for
some people. Remember the old western expression, "the pioneers catch
all of the arrows". Remember also that they end up with all of the
- Modifying a pump to lower the
L3/D4 can mean changing the original
specifications, but the seal and bearings will work
- Installing an oversize stuffing box and
hooking up a suction recirculation line is inconvenient, but it
will dramatically increase the life of most mechanical
- For many years maintenance people have
complained that, "there is never time to do it right but there is
always time to fix it!". That is the same reason heart attack
victims start a sensible diet and exercise program after the heart
attack. There was no time to exercise in the past, but there is
plenty of time to do it now. How would you feel if your supplier
gave you a discrepant part because there wasn't time to get a good
one? Most rotating equipment problems manifest themselves in poor
seal and bearing life. Are you just replacing these items or are
you solving the generic problem that is causing them?
If you are not in a position to make the necessary
decision, team up with somebody that is. There is nothing more
powerful than the combination of an engineer willing to take a chance
on a new idea and a maintenance man prepared to make the decision
One more thought on this subject is to remember
that it is crazy to consider something that might work if nothing
goes wrong. Miracles do happen, but you can't count on
4. Converting a decision to an action will never
occur until it becomes some one's responsibility to carry it out in
specific steps. It is only a wish until a person is chosen and a time
limit is set. You must act or not act, you must never
- Who is supplying the print for the pump
modification? Who will do the machining?
- Who will enter the new parts into the spare
parts system and sign the purchase order for the new
- What is going to happen to the old spare parts
that are now obsolete. Who will take charge of them?
5. Even the best of decisions eventually become
obsolete. You must go and look for your self. Don't even think about
having someone else do the follow-up.:
- You decided to purchase a standard ANSI, ISO
or API pump. Did this solve or increase your seal and bearing
- Should you continue to use solid seals or
designs make more sense?
- Is purchasing an efficient pump increasing
your maintenance problems? It often does. You would probably be
better off with a less efficient design like a double volute type
and solve the shaft deflection problems you are experiencing every
time the pump operates off of its best efficiency point
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