To achieve reliability in any plant, you must stop focusing on mere symptoms of failure and instead concentrate on underlying problems. Here’s practical advice on how to let go of the ‘repair mode’ for the ‘reliability mode’ approach.
Few companies give more than lip service to the concept of “pump reliability.” In fact, there is a disturbingly high percentage of companies that don’t even consider the possibility. Most think it’s going to be either impossible or expensive to achieve. The good news is that neither is true. The first thing needed to achieve pump reliability in any plant is to stop working in “repair mode.” In other words, don’t focus on replacing the bearing when it fails. Instead, find out what caused it to fail and correct that underlying problem.It is also necessary to understand that pump failure tends to be caused by only one or more of four underlying conditions: The wrong pump Improper installation Inappropriate operation Incorrect maintenance By examining this list, it becomes evident that a systematic and practical approach to pump reliability is needed and must involve a number of people from different departments. In fact, it’s typically necessary to cross traditional departmental boundaries in a company in order to assemble the personnel for an effective Reliability Team.
|Ideal pump suction piping allows the pump to receive a smooth, even flow of liquid into the eye of the impeller. |
This team should be a self-managed group that has a clear mandate to increase the reliability of pumping equipment in the plant. It should be responsible for establishing and ensuring compliance with all procedures involved in the creation, operation and maintenance of the pumping system, as well as being empowered to upgrade any and every pump that fails. In addition, members of the team must be fully trained in their various duties as part of the team, regardless of their previous experience. Let’s now consider the four underlying causes of pump failure using this “reliability mode” thinking.
The Wrong Pump
The pump may not be right for the system because the system has changed, because the pump has deteriorated beyond an economical level of redemption or because the pump was inaccurately selected in the first place. If the wrong pump was selected, a complete re-evaluation of system requirements is needed and should be reviewed in detail.
Pump installation requires both hydraulic and mechanical considerations. A pump must be installed in such a position that it will be supplied with the correct pressure and flow characteristics needed for reliable operation. This usually requires the kind of suction piping arrangement, as shown in Figure I, that allows the pump to receive a smooth, even flow of liquid into the eye of the impeller. It is also important that the pump be mounted on a strong base and installed in such a way as to ensure that no external stresses are being imposed by the pipe work.
Regardless of popular opinion to the contrary, the centrifugal pump is a slave to the system. Just because the pump nameplate says it has been designed to deliver 250 GPM at 125 feet of head, doesn’t mean the pump will deliver that amount. The system may not choose to allow the pump to operate at these conditions. Few operations people understand that bearing failure can be a result of the set position of the discharge valve because nobody has bothered to inform them.
The function of a maintenance department is to keep equipment in good condition. This is frequently interpreted as the ability to take a pump apart, replace the worn or broken items with new parts, and put it back together again. When the pump is re-installed, it normally runs as well as it ever did for a while. In most plants, maintenance mechanics are unjustly blamed for many problems. In fact, they do a much better job than is generally realized. That does not mean to say that they don’t make mistakes. The difference is that not only does the maintenance department have to fix problems it creates, but it must also fix the problems that everyone else may have created by purchasing the wrong pump, installing it improperly, and operating it inappropriately. Unfortunately, these mechanics and millwrights are rarely supplied with the information and training they need to help them identify a pump design problem.
Training and Experience
In every area, training is a vital part of the process to improve pump reliability, and it should never be limited to skills training. People who know why they are doing a job always outperform those who simply know how. Even the approach to training must be carefully considered. When I don’t know what I don’t know, I don’t know what I need to know. In fact, if no one has criticized what I’ve been doing for the last 20 years on the job, why would I assume my actions or expertise need to be improved? It is only when I realize that I am not achieving a result that I want, that I’m prompted to change the method by which I’m trying to achieve it. This can only occur when I have identified the desired result and made a commitment to achieve it.
|Few operations people understand that bearing failure can be a result of the set position of the discharge valve. |
It’s also important to keep in mind that having a long-serving team of experienced people in the plant can be a double-edged sword. Individuals are familiar with the equipment they have had to repair repeatedly. However, this leads to the same old cycle of treating the symptom rather than evaluating and coming to terms with the real underlying problem. The reality is that a proper pump reliability program must have corporate commitment and involve a long-term investment and a significant amount of training, not only just to improve skill levels but also to increase awareness of the detrimental ramifications of some of the practices currently considered normal. Ross Mackay specializes in helping companies increase their pump reliability and reduce operating and maintenance costs through his Mackay Pump School, which can be conducted at a client’s facility. He is the author of “The Practical Pumping Handbook” and can be contacted at 905-726-9587 or through his website at www.practicalpumping.com.