Troubleshooting problem causes

In HPLC instrumentation troubleshooting, problems can be classified as follows. Major HPLC problems are discussed under this paragraph, while an extended summary of problem causes and remedy actions are tabulated in the respective tables. 

Discrepancies in performance may be caused by deviations in physical properties of fluids, flow rates, inlet temperatures, mechanical construction of the equipment, or by problems caused during the installation of the equipment. The troubleshooter should first check to see that compositions, flows, temperatures, and physical properties agree with those specified for design. He should then examine the equipment drawings to determine if the problem could lie in the manner in which the equipment was constructed, or in the manner in which the equipment has been installed. After these basic items have been reviewed, the checklist below outlines some questions that should be raised. 

Troubleshooting and Diagnostics (mechanical and non-mechanical problems, determination of probable problem cause, mechanic s responsibilities.)... 

Diagnostic/Troubleshooting Problems If a change in process output (process disturbance or upset) is observed, the cause (change in process input, change in equipment performance) must be identified. 

To review, this relatively simple problem illustrates how there can be multiple possible causes and multiple solutions to a troubleshooting problem The strategy presented here for solving troubleshooting problems was illustrated. 

There are several lessons to be learned from this process troubleshooting problem. As discussed earlier in this chapter, it is inportant not to focus on one possible solution to the exclusion of others. It is inportant to consider as many alternatives as possible. Several possible causes were presented here for the observed process upsets. Wthout detailed measurements and/or simulations, which take more time to perform, the other possibilities could not be ruled out. They would cause the same qualitative trends, but different quantitative values for the upset parameters. 

The activities under interpretation are divided into four categories. Troubleshooting is a procedure to identify and solve a problem in the unit. Hypothesized causes for the observed problems are developed and then tested with appropriate measurements or identification of changes in operating conditions. 

Troubleshooting is described by suggesting possible causes of the more common problems and discussing corrective measures. 

Several causes of V-belt failure and the action required to correct the problem are described in this section. Table 58.6 provides a troubleshooting overview. 

This chapter highlights the common problems, symptoms, and probable causes that may be encountered in troubleshooting FCC units. In addition, a systematic approach is outlined to provide solutions and corrective action. The suggested solutions are necessarily generic but apply to a wide variety of units. 

The best practice in troubleshooting an interface is first to determine that the problem is in the interface. If upon connecting the GC column to an alternate detector, the problem is no longer evident, then it is likely an interface problem. Problems with capillary columns usually involve column plugging. This problem can be alleviated by breaking off a small section at the front of the column. Because plugging can be caused by a cold spot... 

Problems that arise with HPLC experiments are usually associated with abnormally high or low pressures, system leaks, worn injectors parts, air bubbles, or blocked in-line filters. Sometimes these manifest themselves on the chromatogram and sometimes they do not. In the following subsections, we address some of the most common problems encountered, pinpoint possible causes, and suggest methods of solving the problems. You can also refer to the troubleshooting guide in Chapter 12 for possible solutions. 

With the plant interview information, verification of the data, and the completion of the simple calculations, an experienced troubleshooter will develop a set of hypotheses for the root cause of the defect. After the hypotheses are established, a series of experiments need to be developed that accept or reject the hypotheses. Once a hypothesis is accepted via experimentation, then the next step is to develop a technical solution to remove the defect. Often more than one technical solution Is possible. The best technical solution will depend on the cost and time to implement the solution, machine owner acceptance, and the risk associated with the modified process. An accepted hypothesis must drive the technical solution. If a hypothesis is not accepted prior to developing a technical solution, then the troubleshooter may be working on the wrong problem and the defect may not be eliminated from the process. 

Performance information for the incumbent resin was missing from the early parts of the decision-making process. The decision that the technical problem was the performance of the new resin was based on anecdotal information from plant personnel on the performance of the incumbent resin. That is, the plant personnel believed that the reject level for parts made from the incumbent resin was less than 5 %. A statistical analysis of the part defect rates was not performed. This lack of information early in the process allowed the plant manager to propose a poor technical solution without understanding the root cause for the defect. Later in the troubleshooting process, a statistical analysis of the defect rate indicated that the incumbent resin had a defect rate that was statistically equivalent to the new resin. 

This case study was developed with an alternative hypothesis and then a second hypothesis, and the experiments were designed properly to determine quickly the root cause of the defect in the part profile. If the hypotheses and experiments had not been developed properly, the time required to troubleshoot the problem would have increased or the project would have failed. 

Several case studies are presented in the next sections that show some common root causes of contamination in injection-molded parts. In these case studies, the problem is presented in a manner that the troubleshooter would encounter during a trial or information-gathering session. In each case study, the modifications required to fix the process are detailed along with supporting fundamental information. Two of the case studies used (ET) screws to eliminate the defects. ET screws and other high-performance screws will be discussed in Chapter 14. 

It is important to understand admixture-cement and also admixture- admixture interactions so that optimum use of these materials can be made, admixture-cement incompatibility can be prevented, better troubleshooting of field problems is enabled, and the prediction of concrete properties is made possible. In the following pages some examples of problems that arise from admixture-cement and admixture-admixture interactions are cited, and an outline of the physicochemical concepts involved in the interference with cement hydration and interparticle interactions that limit admixture performance, and cause incompatibility and field problems is presented. 

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