Pump Doesn't Operate?
Replace or Repair: That Is The Question.

A well engineered and properly installed submersible pump or dry-pit pump is one of the most reliable and trouble-free components of any water or wastewater pumping system. However, as with any mechanical device the day will come when it does not operate properly. It is at this point that several questions must be addressed.

• Number one: can the problem be identified?
• Number two: can the problem be fixed?
• Number three: how much will it cost?

Identification of the problem is often the most difficult of the three questions. Success in identifying the problem or problems-as there may be more than a single problem involved-depends on knowledge, experience, intuition, luck and the nature of the problem.

The answers to questions number two and three are usually intertwined, as almost anything can be fixed-but at what cost? In practice, the question of cost quickly moves to the forefront of the decision-making process. This usually focuses down to whether it is most cost-effective to replace or repair. One rule-of-thumb often quoted is "If it costs more than half the cost of a total replacement to repair, it should be replaced." This is generally good advice, but it does depend heavily on the proper identification of the problem (and perhaps many other circumstances, such as pending system changes, etc.). For example, if the problem of a pump not starting lies in the controller, and is a connection problem, replacement of the pump will not solve the problem. In this case replacement would be a costly mistake, while the repair would be relatively inexpensive.

Sometimes, identification of the problem seems obvious. However, in most every situation it is best to follow a very deliberated protocol or process in the identification of the problem. This is true because there may be more than a single problem or the obvious problem may be a result of a less obvious problem. For example, overheating or failure may be the result of excessively low voltage or lack of continuity in wiring or motor windings may be the result of excessively high voltage. In either case, replacement of the pump would not solve the problem. The incorrect voltage levels would quickly damage the new replacement pump, also.

Quality pumps are engineered to provide many, many years of trouble free service. Many EMU pumps have been in service and untouched for more than 15 years.

Measurement of pump vital signs will identify the nature of the problem and allow an estimate of the cost of repair. If the repair costs are less than half the cost of a new unit, repair is usually the most cost-effective choice.

Typically, it is best to be systematic and to record findings carefully in writing. Most importantly, it is always imperative to put safety first in all investigations associated with problems-there can be surprises, especially while the unknown problem remains unresolved.

With pumps there are three basic types of problems: electrical, mechanical and hydraulic. In the course of an investigation of a pumping problem each of the three areas should be investigated and performance to specifications confirmed.

Electrical

Electrical problems may be associated with power supply or internal to the pump. Since external power supply components are usually easier to access, they provide a good place to start the investigation process. Prescribed supply voltage levels should be verified. If incoming voltage levels are found to be inconsistent with prescribed levels, this problem should be addressed before proceeding further. If voltage levels are within acceptable ranges then it is appropriate to shut off power to the controller and investigate further. With breakers open and the flow of current halted, all electrical components associated with the electrical supply should be examined visually for any tell-tale evidence of overheating, such as burn-marks or discoloration. Next, while referring to system schematics, continuity and resistant values should be checked and confirmed with available documentation. Evidence of corrosion, poor connections and line-breaks should be explored. If all is in order, the electrical investigation should move to the pump terminals, where the continuity of the windings should be checked. If a short is identified in the windings, it is almost certain that the pump will have to be removed and the issue of costs for replacement or repair will have to be carefully evaluated. If on further examination, all castings are in good condition, the repair of the pump may be practical and cost-effective. None-the-less, the root cause of the wiring failure must be identified to avoid a repeat of the event. Root causes of winding shorts can range from lightening (which will usually show itself in the controller, first); to seal failure; or from water intrusion at the entrance to the terminal to excessive motor age.

Mechanical

Mechanical problems can be the result of wear (seal or bearing failure) resulting from years of use or lubrication problems or, simply, physical obstructions (such as debris lodged or entangled in the impeller). Again, identification of root causes is important if repeat problems are to be avoided. With most purely mechanical problems the issue of repair or replacement can be quickly settled by the cost rule of repair if it is less than half the cost of replacement.

Hydraulic

Typically, hydraulic problems are the direct result from either electrical or mechanical problems. However, hydraulic problems can result from a worn, broken, or incorrectly specified impeller. In this case, replacement is straightforward and reasonably economical. If wear problems are a reoccurring problem, special hardened impellers are available that greatly extend replacement cycles. Occasionally, hydraulic problems can be caused by air or gas in the system and in such cases the air or gas has to be removed and the root cause has to be eliminated. Though it should go without saying, if hydraulic problems exist, it is important to ensure that all system valves are in the proper position and that the pump is properly seated on the discharges.

Quality Pumps Rarely Need To Be Repaired

Although this brief article serves only as an overview of pump problem assessment, it is hoped that it will underscore the need to be methodical in identifying pump problems, and most importantly that it will encourage the purchase of quality, well engineered pumping equipment in the first place. Because, as every pump specialist will tell you, quality pumping equipment is always the most cost-effective choice in the long run.