11 an Expert System for Pump Diagnosis

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Session F2G

0-7803-8552-7/04/$20.00 2004 IEEE October 20 23, 2004, Savannah, GA

34th

ASEE/IEEE Frontiers in Education Conference

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PUMPX: An Expert System for Pump DiagnosisMario A. Garcia 1, John Clements2, and William Shelton3

1 Mario A. Garcia, Texas A&M University-Corpus Christi, Computing and Mathematical Sciences, Corpus Christi TX, 78413, [email protected] John Clements, Texas A&M University-Corpus Christi, Computing and Mathematical Sciences, Corpus Christi TX, 784133 William Shelton, Texas A&M University-Corpus Christi, Computing and Mathematical Sciences, Corpus Christi TX, 78413

Abstract - Diagnosing problems with centrifugal pumps

usually requires personnel with extensive experience oreducation. Centrifugal pumps represent the largest power

consumption of any type of liquid movers in

industrialized countries. Diagnosis of problems with

recommendations from a computerized assistant would be

highly useful. This paper describes the implementation of

PUMPX, an expert system for diagnosis of pump

problems and for recommendation of corrective action.

Four main symptoms are included: vibration/noise, high

temperature, leaks and low performance. The use of this

program can lead to utilization of lower experience

personnel for diagnosis and can be used for training. The

correct and timely diagnosis and correction of pump

problems will lead to reduced power consumption and

avoid unnecessary expenditures for upgrades.

Index Terms - Centrifugal Pumps, Expert System, InxightTree. Knowledge Acquisition.

INTRODUCTION

This expert system is intended to assist in the diagnosis ofcentrifugal pump problems. Pumps are used to move liquidsand constitute a major consumer of energy in industrializedcountries. Pump capacity range is very wide. Small capacitypumps are used for medical and additive uses, taking as manyas 17 days to pump one gallon. Large pumps are used inirrigation, municipal water supply and industrial uses. Theseare available in individual capacity as much as 100,000gallons per minute, using many thousands of horsepower.Pumps can be divided into two classes: dynamic and positivedisplacement [13]. Centrifugal pumps are in the dynamicclass. Centrifugal pumps may be divided into axial flow,mixed flow, and peripheral. This expert system is limited toaxial flow centrifugal pumps.

As pumps are used, they may wear or develop variousmechanical problems. Experts are needed at each installationto diagnose these problems for repair, or consultants need tobe employed for diagnosis. Many programs exist for theselection of pumps for new installations or upgrades. Oneexample is from Goulds Pumps [8]. Another is available for

the Palm hand held device. The mechanical and processengineering literature is replete with discussions of pumps,selection methods, and diagnosis methods, such as checklists [2, 13, 15]. Some of these methods include categories

of symptoms and then items to check and/or causes. The goal

of most of these systems is to identify the root cause [3].Need For Expert System

As noted above, experts are needed to diagnose problemswith centrifugal pumps. These may be engineers with formaltraining, experienced operators, experienced maintenancepersonnel or consultants. Many industrial installations willhave experts. Their time is, of course, limited and theycommand higher compensation. Smaller installations, forexample, hospitals and schools, have limited resources. Thisexpert system is designed to allow training of individuals,help for smaller installations and use by non-experts on adaily basis. Durkin [7] indicates that 25% of all expertsystems are used for diagnosis and 14% are used inmanufacturing. He reports that DuPont Chemical Companywas saving $100,000,000 per year by using expert systems.

PUMP SYSTEMS

This expert system is limited to axial flow centrifugal pumps.A typical pump and electric motor is shown in Figure 1. Thepump is on the right hand side, motor is on the left. Inbetween these two devices, is the shaft coupling. This isrequired to transfer all the horsepower and torque from themotor to the pump. These are bolted to the baseplate, thechannel shaped plate in Figure 1. The baseplate is normallyattached to a concrete block called the base and secured bybolting and adding cement grout between the two. The base,baseplate and grout add rigidity to the pump/motor andprevent excessive motion between the pump/motor and thesurrounding piping.

A centrifugal pump works by rotating a plate, called animpeller, with liquid entering in the center and exiting theouter rim. This imparts velocity to the liquid. A crosssection of a cantilevered, horizontal, end suction pump isshown in Figure 2. Liquid enters via the horizontal opening(1) and contacts the rotating impeller (2). It is confined bythe casing (3), exiting via the discharge port (4). Theincrease in velocity is converted to an increase in pressure.Behind the impeller is the back plate (5). The shaft (6) iscarried by bearings (7). These bearings typically run in an oil

bath (8). There may be a cooling chamber for the bearing oil(9). The rotating shaft and stationary parts are connected viaa seal (10). All of these are subject to wear and may need tobe examined, repaired and/or replaced.


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FIGURE 1HORIZONTAL CENTRIFUGAL PUMP AND MOTOR

Low performance is evaluated by comparing currentperformance with manufacturers data. Manufactures data iscontained on a pump curve. A typical pump curve is shownin Figure 3. This graph contains a wealth of informationincluding, the pump manufacturers name, pump size andmodel number, speed, smallest and largest impeller size and

impeller version. This is basically a plot of pressuredeveloped in feet of liquid pumped (1) versus the quantity ofliquid pumped (2). Each different impeller size produces adifferent head/flow curve (3). Plotted on this graph is thehorsepower required at each head/flow point (4) and Netpositive suction head required (NPSHR) is plotted versus flow(5).

Testing usually consists of placing a pressure gauge onthe suction and discharge sides of the pump while the liquidis flowing. At the same time, power readings are taken. Thisis repeated while the discharge valve is closed. This lattertest yields the values at dead head. The pressure in psi ismultiplied by 2.31 feet per psi and divided by the liquid

specific gravity to yield feet of liquid.These two values are subtracted to give the increase in

feet of liquid from the pump, the pump delta value. Thisexpert system prompts for the pressure gauge readings andcalculates the feet of liquid. Many diagnoses can be madefrom these results. For example, if the delta is lower than thatshown on the curve or that size and speed of impeller, theimpeller may be worn; if the dead head delta is low and thepower is high, it may show an excessive amount of clearancebetween the impeller and back plate.

As the impeller is rotated, it generates a low pressurearea in the center, with an increase at the periphery. As theliquid flows into the center of the impeller, flow generates

pressure drop. If the pressure drop is high enough, it cangenerate vaporization of the liquid. This is cavitation andleads to low flow and excessive wear to the impeller.

Cavitation can be caused by a restriction in the suctionpiping, low level in a feed tank or by a hot liquid. Acalculation is used to determine if the Net Positive SuctionHead (NPSH) required by the particular pump exists. NPSHRis calculated by taking the atmospheric pressure andconverting to feet of liquid, adding the level in the feed tank,subtracting the loss in the suction piping and subtracting thevapor pressure of the liquid. The expert system prompts forall these values and calculates the result, the Net PositiveSuction Head Available, NPSHA. TheNPSHA must exceedthe NPSHRor there will be acavitation problem. The expertsystem recommends action to correct this, if found.

This expert system works by eliciting responses toobserved problems. Some of these symptoms are solvable bymechanical correction, others require process change, such asraising the feed tank level. The categories of symptoms inthis expert system are: vibration/noise, overheating, leaks andlow performance.

FIGURE 2HORIZONTAL CENTRIFUGAL PUMP CROSS SECTION

EXPERT SYSTEMS

Expert systems are computer programs that incorporate alarge amount of knowledge in a very specific field and areused to give advice or solve problems. These incorporateknowledge of experts and attempt to simulate the reasoningprocess. These programs contain a heuristic to imitate theexperts use of the knowledge and seek to distribute theexperts knowledge and reasoning to a wider audience.Hall [9] indicates the most successful expert systems areapplied to problems with limited domains and well-defined

expertise.


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FIGURE 3PUMP PERFORMANCE CURVE

An expert system should exhibit high performance andreliability, be flexible and user friendly and be well tested.Acceptance by users is highly dependent on and easy-to-useuser interface, correctness of results and perception that the

expert system reduces the workload and/or has ademonstrable savings [5,12,17.] This expert system is rule-based. Rules are evaluated to be true or false and it employsthe closed world assumption that if something is not knownto be true then it is false. This assumption is good forphysical problems according to Hopgood [10]

Knowledge Acquisition

One of the authors of this paper works in the industrial fieldand has worked in the application for many years. A numberof references were consulted concerning pump applicationand diagnosis [2,13,15]. Individual manufacturers oftenproduce troubleshooting guides for their products. Cooke[6,8] summarizes the acquisition interview process inexcellent form. Many check lists and other aids have beendeveloped to assist the technician. Check lists, and other aidshave been summarized in a set of flowchart style blockssimilar to decision trees [1]. These were then used toestablish rules for the expert system. Also these were used toverify the expert system.

Knowledge Representation

The various levels in the flowcharts have been representedin Inxight Tree Studio [11], as it is shown in figure 4. Mainsymptoms are: vibration/noise, overheating, leaks and lowperformance. Each of these symptoms then results in a seriesof questions that leads to a diagnosis or no diagnosisresponse. The expert system also may recommendcorrections.

FIGURE 4.KNOWLEDGE REPRESENTATION IN INXIGHT TREE

Knowledge Implementation

TPUMPX was implemented in CLIPS. Rules weredeveloped from the flowchart style block structure. The useris prompted for the main symptom, such as vibration, lowflow, etc. and then the expert system asks the user questions.From these responses, a particular branch of the flowchart isfollowed and then the diagnosis response given or a nodiagnosis response given. CLIPS code for the main menuand example rules are shown in figure 5.

(defrule main-menu (declare (salience 100))?f1

(bind ?response (ask-question"What type of problem would you like to diagnose?1. Overheating2. Poor Performance3. Noise / Vibration4. Fluid Leak5. Exit PumpExPlease choose an option (1-5):" 1 2 3 4 5))(switch ?response(case 1 then (modify ?f1 (main-symptom overheating)))


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(case 2 then (modify ?f1 (main-symptom performance)))(case 3 then (modify ?f1 (main-symptom vibration)))(case 4 then (modify ?f1 (main-symptom leak)))(case 5 then (halt))(default none)))

FIGURE 5

A RULE IN CLIPS

Testing

This expert system was tested by following each branch inthe Inxight Tree answering each question presented byPUMPX in each possible way and checking if it gave thecorrect response based on the flowcharts. In each case, it didgive the correct response.

RESULTS AND CONCLUSIONS

PUMPX incorporates many of the diagnostic check lists andflowcharts of manufacturers, the literature and experts. Itincludes in one program, a method for trained and untrained

people to obtain probable diagnosis with a high level ofconfidence. It includes a user-friendly interface. It operatesfast with currently available personal computer hardware.

This expert system is based on rules. Another approachis case-based reasoning where additional instances and resultsare input and the expert system develops rules based on thesesuccessful solutions [4,14]. This might be a useful extensionto this expert system.

A recent example is: a pump was noisy, producing awidely swinging pressure, the control valve was 100% openand had a reputation of not working. PUMPEX quicklydiagnosed the problem from the swinging pressure and noiseand diagnosed that the feed tank level might be low. The

problem was corrected and the Pump has been performingwell. The opinion of others prior to this diagnosis was thatthe pumps had to be replaced or the discharge line replaced ata cost of at least $50,000. This cost was saved. If this expertsystem had been in place, operating personnel could havemade this diagnosis and fixed it immediately. It is believedthis condition existed for at least a year.

Future Work

This expert system would be a natural application fornetwork. Also, it would be good to have the ability to runthis on a local tablet personal computer or handheld Palmtype personal digital assistant. Even more useful, would be to

use this at the pump with the manufacturers pump curve pre-loaded or accessible on the handheld device. All of thesewould require implementation on a Web-based language suchas JESS, access to the facilities manufacturers database andpossibly a wireless network.

REFERENCES

[1] [Allmuallim, Hussein, Kaneda, Shigeo and Akiba, Yasuhiro,Development and Applications of Decision Trees in Leondes,Cornelius T, Expert Systems The Technology of Knowledge

Management and Decision Making for the 21stCentury, Volume 1,Academic Press, San Diego, California, 2002, pp 54-75.

[2] Baumiester, Theodore, Avallone, Eugene A. and Baumiester, TheodoreIII,Marks Mechanical Engineers Handbook, McGraw-Hill, NewYork, 1996.

[3] Bellinger, G.,Root Cause Analysis, available on the Internet atwww.outsights.com/systmes/rca/rootca.htm, accessed April 2, 2003.

[4] Bergmann, Ralph, Breen, Sean, Goker, Mehmet, Manago, Michel andWess, Stefan,Developing Industrial Case-Based Reasoning

Applications, The INRECA Methodology, Springer, 1999, pp 9-34.

[5] Bobrow, D. G., Mittal, S. and Stefik, M. J. Expert Systems: Perils andPromise, Communications of the ACM, vol 29, number 9 [1986].

[6] Cooke, Nancy J., The Elicitation of Domain-Related Ideas; Stage Oneof the Knowledge Acquisition Process, in Ellis, Charlie, Expert

Knowledge and Explanation, the Knowledge-Language Interface, EllisHorwood, Chichester, West Sussex, England, 1989, pp 58-75.

[7] Durkin, John, History and Applications and Tools andApplications, in Leondes, Cornelius T.,Expert Systems TheTechnology of Knowledge Management and Decision Making for the

21stCentury, Volume 1, Academic Press, San Diego, California, 2002,pp 1-50.

[8] Goulds Pumps, Division of ITT Industries, Pump Selection Software,available on Goulds Web site at http://www.goulds.com/software.asp,accessed April 27, 2003.

[9] Hall, Lawrence O. and Kandel, Abraham, The Evolution from ExpertSystems to Fuzzy Expert Systems, in Kandel, Abraham, ed.Fuzzy

Expert Systems, CRC Press, Boca Raton, Florida 1992, pp 3- 22.

[10] Hopgood, Adrian A., Intelligent Systems for Engineers and Scientists,CRC Press, Boca Raton, Florida, 2001, pp 1- 45, 265-311.

[11] Inxight Studio Tree Software, Inxight Corporation, available at www.inxight.com, accessed April 1, 2003.

[12] Jagodzinski, A. P. and Holmes, S. H., Expert Systems Acceptability:Human and Organizational Contexts of Expert Systems, in Ellis,Charlie, Expert Knowledge and Explanation, the Knowledge-Language

Interface, Ellis Horwood, Chichester, West Sussex, England, 1989, pp226 241.

[13] Karassik, Igor J., Krutzsch, William C., Fraser, Warren H. and Mesina,Joseph P.,Pump Handbook, McGraw-Hill, New York, 1986, chapters1, 2, 8, 12, and 13.

[14] Leake, David B. editor, Case-Based Reasoning, Experiences, Lessonsand Future Directions, AAIA Press/The MIT Press, Menlo Park,California, 1996.

[15] Perry, Chemical Engineers Handbook, Seventh Edition, MacGraw-Hill, New York 1987.

[16] Process Ace Software,Pump Calculations for the Palm, detailsavailable via the Internet atwww.processacesoftware.com/pump_calulations_help.html, accessedApril 2, 2003.

[17] Prerau, David S.,Developing and Managing Expert Systems, ProvenTechniques for Business and Industry, Addison-Wesley, Reading,Massachusetts, 1990, pp 100- 106.

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11 an Expert System for Pump Diagnosis