CENTRIFUGAL PUMP TROUBLESHOOTING

PUMP PROBLEM AREAS SEALS BEARINGS NOISE & VIBRATION LACK OF FLOW LACK OF HEAD BROKEN SHAFTS OVERLOADED MOTOR ETC. THESE ARE ONLY A FEW OF THE MANY AREAS THAT CAN BECOME A PROBLEM

CAUSES OF PUMP PROBLEMS PUMP INCORRECTLY SIZED MISALIGNMENT CAVITATION PIPING DESIGN LUBRICATION FOUNDATION ETC THESE ARE ONLY A FEW OF THE MANY CAUSES OF CENTRIFUGAL PUMP PROBLEMS A “TROUBLESHOOTING GUIDE” IS AVAILABLE IN THE IOM. I HAVE RE-MADE THAT GUIDE IN A DIFFERENT FORMAT. IT IS INCLUDED AT THE END OF THIS PRESENTATION.

FOCUS ON MATCHING THE PUMP & SYSTEM FIND OUT WHERE THE PUMP IS OPERATING ON THE CURVE OFTEN THE PUMP WILL OPERATE WITH FEWER PROBLEMS BY OPERATION CLOSER TO THE BEP (BEST EFFICIENCY POINT) WE’LL LOOK AT THE COMMON PROBLEM OF A CAVITATING PUMP THE FOCUS OF MY TROUBLESHOOTING PRESENTATION WILL BE ON GETTING THE PUMP AND SYSTEM TO MATCH THERE ARE NO “ONE SIZE FITS ALL” SOLUTIONS TO ANY PROBLEM. ALL SOLUTIONS WILL DEPEND ON THE PARTICULAR PUMP AND SYSTEM. LATER WE WILL LOOK AT AN EXAMPLE OF A CAVITATING PUMP AND WAYS TO CHANGE THE SYSTEM CURVE OR WHERE WE ARE OPERATING ON THAT CURVE.

NOTE LOCATION OF THE BEP (BEST EFFICIENCY POINT) THIS IS WHERE THE RADIAL LOADS ARE AT THEIR MINIMUM THIS IS WHERE THE FLOWS ENTERING THE IMPELLER BEST MATCH THE VANES THIS IS WHERE THE FLOWS ENTERING THE THROAT & DIFFUSER BEST MATCH THE CASING CUTWATER VIBRATION IS AT A MINIMUM NOTE THE MRF (MINIMUM RECOMMENDED FLOW) LINE NOTE THE NPSHR LINE. THE HIGHER THE FLOW THE HIGHER THE NPSHR. NPSHR INCREASES RAPIDLY TO THE RIGHT OF BEP. CAVITATION PROBLEMS INCREASE RAPIDLY TO THE RIGHT OF BEP AS A RESULT. POWER IS AT MAXIMUM AT THE END OF THE CURVE

THE SYSTEM CURVE SHOWN IN GREEN REPRESENTS A TYPICAL SYSTEM NOTE THE 30 FOOT STATIC HEAD (AT ZERO FLOW) EVERYTHING ABOVE THE 30 FOOT STATIC HEAD LINE IS THE FRICTION COMPONENT OF THE SYSTEM HEAD CURVE. THE PUMP WILL OPERATE WHERE THE PUMP CURVE AND THE SYSTEM HEAD CURVE MEET

WHY IS THE SYSTEM CURVE IMPORTANT ? SYSTEM CURVE IS FUNDAMENTAL TO EVERYTHING THE PUMP DOES CRITICAL TO UNDERSTAND THE STATIC AND FRICTION COMPONENTS OF THE SYSTEM CURVE FOR OPTIMIZING – WE ASK IF WE CAN CHANGE THE SYSTEM CURVE OR WHERE WE ARE OPERATING ON IT

PUMP AND SYSTEM PUMP DOES NOT CONTROL THE SYSTEM THE SYSTEM CONTROLS THE PUMP THE PUMP SIMPLY REACTS TO WHAT THE SYSTEM TELLS IT TO DO THERE IS NO LIMIT TO THE POSSIBLE SYSTEM CONFIGURATIONS

NOTE THE THREE SYSTEM HEAD CURVES. EACH HAS A 30 FOOT STATIC HEAD NOTE THE THREE SYSTEM HEAD CURVES. EACH HAS A 30 FOOT STATIC HEAD. EACH HAS A DIFFERENT FRICTION COMPONENT. NOTE THE LEFT SYSTEM HEAD CURVE WILL MAKE THE PUMP OPERATE BELOW THE MINIMUM RECOMMENDED FLOW. CONSIDER THE POSSIBLE PROBLEMS WITH INCREASED DEFLECTION, AND VIBRATION WHAT ABOUT POSSIBLE OVERHEATING? THE SYSTEM CURVE ON THE RIGHT IS SUBJECT TO CAVITATION, VIBRATION AND DEFLECTION. WHAT ABOUT A MOTOR THAT IS NOT SIZED TO COVER THE END OF THE CURVE?

THIS SHOWS TWO SYSTEM HEAD CURVES WITH DIFFERENT STATIC HEADS. ONE CURVE HAS ALMOST NO FRICTION HEAD ONE CURVE HAS NO STATIC HEAD THIS PUMP WILL REACT VERY DIFFERENTLY IN THESE TWO SYSTEMS IF MINOR CHANGES ARE MADE TO THE RPM OR IMPELLER DIAMETER.

DEVELOP SYSTEM CURVE FROM FIELD MEASUREMENTS CAPTURE CRITICAL ELEMENTS OF THE SYSTEM HOW? REVIEW PI&D AND PIPING ISOMETRICS TALK TO OPERATORS WALK DOWN THE SYSTEM & RECORD ALL COMPONENTS CALCULATE TDH (STATIC & FRICTION) A LOT OF TEDIUS WORK. IT’S EASY TO MISS SOMETHING. WE ALSO HAVE A PUMP INSTALLED IN A SYSTEM AND CAN TAKE SOME PRESSURE MEASUREMENTS TO DETERMINE THE SYSTEM CURVE

CONSIDER THIS SYSTEM AS AN EXAMPLE: TRANSFERING WATER FROM ONE TANK TO ANOTHER FROM THE PUMP INSTALLED IN A SYSTEM WE CAN LEARN A LOT ABOUT THE SYSTEM CURVE. REMEMBER THAT THE PUMP CURVE AND THE SYSTEM CURVE HAVE A COMMON POINT AT THE PUMP’S OPERATING POINT. WE NEED THE TWO COMPONENTS OF THE SYSTEM CURVE: SYSTEM STATIC HEAD SYSTEM FRICTION HEAD WE ALSO NEED A FLOW MEASUREMENT FROM THE “SYSTEM” OR A PUMP CURVE TO ESTIMATE THE FLOW

SYSTEM STATIC HEAD STATIC HEAD IS THE TOTAL OF THE ELEVATION AND PRESSURE COMPONENTS HSTATIC= (2.31/SG) X (P5-P1) + Δ ELEVATION HSTATIC= (10.2/SG) X (P5-P1) + Δ ELEVATION (metric constant) (PRESSURE COMPONENT IS ZERO IF THE TANK IS OPEN TO THE ATMOSPHERE) ESTIMATE THE ELEVATION DIFFERENCE FROM DRAWINGS, DIRECT MEASUREMENTS, PRESSURE REASINGS, ETC. DETERMINE THE PRESSURE COMPONENT FROM PRESSURE READINGS, TALK TO OPERATORS REMEMBER THAT IF A TANK IS OPEN TO THE ATMOSPHERE, THE GAGE PRESSURE IS ZERO SG = SPECIFIC GRAVITY P1 & P2 ARE IN PSI

CONSIDER THIS SYSTEM AS AN EXAMPLE: TRANSFERING WATER FROM ONE TANK TO ANOTHER FROM THE PUMP INSTALLED IN A SYSTEM WE CAN LEARN A LOT ABOUT THE SYSTEM CURVE. REMEMBER THAT THE PUMP CURVE AND THE SYSTEM CURVE HAVE A COMMON POINT AT THE PUMP’S OPERATING POINT. WE NEED THE TWO COMPONENTS OF THE SYSTEM CURVE: SYSTEM STATIC HEAD SYSTEM FRICTION HEAD WE ALSO NEED A FLOW MEASUREMENT FROM THE “SYSTEM” OR A PUMP CURVE TO ESTIMATE THE FLOW

SYSTEM FRICTION HEAD HTOTAL = HSTATIC + HFRICTION HFRICTION = HTOTAL – HSTATIC WE CAN MEASURE THE PUMP’S TOTAL HEAD FROM P2 AND P3 HTOTAL = (2.31/SG) X (P3 – P2) (use 10.2 as constant for metric calculation) REMEMBER TO ADD VELOCITY HEAD IF THE PIPE SIZE AT P3 & P2 LOCATIONS ARE A DIFFERENT SIZE ADD ANY GAGE ELEVATION CORRECTION TO READINGS

SYSTEM CURVE WE HAVE TWO POINTS ON THE SYSTEM HEAD CURVE FILL IN THE COMPLETE CURVE WITH THE FOLLOWING RELATIONSHIPS: K=(HTOT1-HTOT2)/(Q12-Q22) = SYSTEM LOSS COEFFICIENT HFRICTION = K X Q2 HTOTAL = HSTATIC + HFRICTION

Now that we have an accurate system curve we can decide what changes are possible or necessary to help solve the “problem”.

WAYS TO REDUCE FLOW CUT DOWN IMPELLER DIAMETER DECREASE PUMP SPEED THROTTLE WITH DISCHARGE VALVE THROTTLE WITH ORIFICE IN DISCHARGE PIPE INCREASE FRICTION LOSS IN DISCHARGE PIPE NOTICE THAT THE FIRST TWO, BY THEMSELVES, WORK WITH THE EXISTING SYSTEM HEAD CURVE THE REST CAN BE USED TO CHANGE THE SYSTEM TO ALLOW THE PUMP TO OPERATE ON A MORE FAVORABLE OPERATING POINT

WAYS TO INCREASE FLOW INCREASE IMPELLER DIAMETER INCREASE PUMP SPEED REDUCE FRICTION LOSS ADD RECIRCULATION LINE BACK TO SUCTION TANK NOTICE THAT THE FIRST TWO, BY THEMSELVES, WORK WITH THE EXISTING SYSTEM HEAD CURVE THE SECOND TWO CAN BE USED TO CHANGE THE SYSTEM TO ALLOW THE PUMP TO OPERATE ON A MORE FAVORABLE OPERATING POINT

ALTERNATIVE THREE GAGE METHOD TOTAL SYSTEM HEAD CAN ALSO BE ESTIMATED IF THE P4 PRESSURE DOWNSTREAM OF THE MAIN THROTTLING VALVE IS AVAILABLE P2 AND P3 IS ALSO NEEDED NEED TO HAVE: PUMP CURVE, PUMP SIZE, EXACT IMPELLER DIAMETER, THROTTLING VALVE, THREE PRESSURE GAGES

CONSIDER THIS SYSTEM AS AN EXAMPLE: TRANSFERING WATER FROM ONE TANK TO ANOTHER FROM THE PUMP INSTALLED IN A SYSTEM WE CAN LEARN A LOT ABOUT THE SYSTEM CURVE. REMEMBER THAT THE PUMP CURVE AND THE SYSTEM CURVE HAVE A COMMON POINT AT THE PUMP’S OPERATING POINT. WE NEED THE TWO COMPONENTS OF THE SYSTEM CURVE: SYSTEM STATIC HEAD SYSTEM FRICTION HEAD WE ALSO NEED A FLOW MEASUREMENT FROM THE “SYSTEM” OR A PUMP CURVE TO ESTIMATE THE FLOW

THREE GAGE METHOD DIFFERENCE BETWEEN P3 AND P2 IS THE PUMP’S TDH DIFFERENCE BETWEEN P4 AND P2 IS THE SYSTEM TDH ADD VELOCITY HEAD IF THE PIPE SIZE AT P3 & P2 LOCATIONS ARE A DIFFERENT SIZE ADD VELOCITY HEAD IF THE PIPE SIZE AT P4 & P2 LOCATIONS ARE A DIFFERENT SIZE ADD ANY GAGE ELEVATION CORRECTION TO ALL READINGS

THREE GAGE METHOD RECORD READINGS WITH FULLY OPEN VALVE WITH PUMP CAVITATING RECORD READINGS WITH VALVE THROTTLED SO THERE IS NO CAVITATION DETERMINE THE PUMP TDH WHERE THE CAVITATION STOPS DETERMINE THE SYSTEM TDH WHERE THE CAVITATION STOPS USE THE PUMP CURVE AND THE PUMP TDH FROM STEP 3 TO DETERMINE THE FLOW WHERE THE CAVITATION STOPS RESIZE THE PUMP/IMPELLER TO MATCH THE FLOW AND SYSTEM HEAD FROM STEP 5 ADD VELOCITY HEAD IF THE PIPE SIZE AT P3 & P2 LOCATIONS ARE A DIFFERENT SIZE ADD VELOCITY HEAD IF THE PIPE SIZE AT P4 & P2 LOCATIONS ARE A DIFFERENT SIZE ADD ANY GAGE ELEVATION CORRECTION TO ALL READINGS

GOTCHA’S GAGE READINGS IN DIFFERENT SIZE PIPE AND FAILURE TO CONSIDER PIPE VELOCITY HEAD FAILURE TO CONSIDER STATIC HEAD DIFFERENCE IN GAGE READINGS CONSIDER WAYS TO KEEP YOURSELF OUT OF TROUBLE IN TAKING READINGS AND INTERPRETATION OF THE DATA AN 8X10 PUMP AT 2000 GPM HAS A VELOCITY HEAD DIFFERENCE OF 1.5 FEET – NOT A BIG DEAL A 1X2 PUMP AT 150 GPM HAS A VELOCITY HEAD DIFFERENCE OF 45 FEET - COULD BE SIGNIFICANT CORRECT GAGE READINGS TO A COMMON ELEVATION – LIKE THE CENTERLINE OF THE PUMP

MORE GOTCHA’S PUMP HEAD CAPACITY CURVE DEVELOPED AT A DIFFERENT SPEED INACCURATE PRESSURE GAGES INACCURATE FLOW METERS PUMP SPECIFIC CURVE NOT EQUAL TO GENERIC CURVE IMPELLER, OTHER PARTS WORN NO CURVE AVAILABLE / DON’T KNOW IMPELLER DIAMETER ACTUAL VS RATED SPEED. PUBLISHED CURVE AT 1750 BUT PUMP IS RUNNING CLOSER TO 1800