A Centrifugal Pump Before (On Left)

and

After Repairs (On Right).

 

 

 

Nobody knows the trouble I've seen

("Nobody Knows the Trouble I've Seen," a spiritual sung by many downtrodden souls)

 

HOW TO TROUBLESHOOT PUMPS THAT ARE MOTOR DRIVEN 

 

Quickie Review of the Centrifugal Pump-Motor Rotating Equipment Combo

WAY TO GO!

Brilliant PTOA Readers and Students ...

who are reading the PTOA Segments in the intended sequential order ...

now possess a complete and fundamental understanding of the form and function of each type of hardware component that must work as designed and intended so that a Centrifugal Pump-Motor Driver combo can successfully infuse the PV Pressure into a flowing process liquid.

Ergo,

At this juncture no PTOA Reader or Student should have any problem identifying the protective housing for each type of functional hardware in a Centrifugal Pump being driven by a Motor.

Challenge yourself!

Scan the two nearby photos depicting Real World, installed and functioning Centrifugal Pumps and Motors and identify each of the components:

• A Centrifugal pump (PTOA Segments #173 through #176).
• The pump's Inlet and Discharge process lines (PTOA Segments #163 and #164).
• The pump Inlet and Discharge Block Valves (PTOA Segment #164).
• The pump's Stuffing/Packing Box (PTOA Segment #181).
• The pump's Bearing Box (PTOA Segments #182 and #183 and #184)
• The pump's Coupling (PTOA Segment #185)
• The pump's electric Driver … which is called a Motor (PTOA Segments #187, #188, and #189).

 

While taking this trip down Memory Lane why not make a stop way, way back at the beginning of the PTOA PV Pressure Process Industry Equipment Focus Study which was first introduced in PTOA Segment #138?

Because way back then is when PTOA Readers and Students first learned that the main function of the  expensive and complex Process Industry equipment categorized as Rotating Equipment  …

for example Centrifugal Pumps and their Drivers …

is to infuse the PV Pressure into a fluid so that a Pressure Differential (ΔP) is generated.

Certainly every PTOA Reader and Student knows by now that The Universe demands that a Pressure Differential (ΔP) exist before any fluid can flow or circulate on Earth!

PTOA Segment #165 explained why pumps are used to create or restore  that crucial Pressure Differential (ΔP).

So pumps make it possible for liquids to flow long distances through piping systems.

And while flowing through piping systems Friction (featured in PTOA Segment #177) is constantly chomping up the PV Pressure ...

and would reduce ΔP to nothing … hence stopping flow!

Dang it!

All of the above reviewed information means that the important function of infusing the PV Pressure into a liquid via a Pump  ...

 

or any other Rotating Equipment driven by a Motor ...

 

will not be possible if that Motor were not functioning!

 

The purpose of this PTOA Segment #190 is to provide a list of troubleshooting steps that can be used to analyze and solve electrically driven pump problems.

 

Orderly Troubleshooting

Process Operators are responsible for analyzing pump problems up until the decision is made to disassemble the pump … which is the Mechanical Technician's wheelhouse.

Disassembling a pump is a costly endeavor and a step not taken unless absolutely necessary.

Prior to disassembling a pump, the best Process Operators work with Electricians, Instrument Techs, and Mechanics to be absolutely certain that disassembly is necessary. .

The "How to Troubleshoot a Motor" guidelines are listed below and there are three noteworthy statements to make about the list:

•  PTOA Segment #190 provides positive proof that not every valuable document has been translated from the printed page onto the internet. The troubleshooting guidelines featured below are paraphrased from a manual which once upon a time was distributed by U.S. Electrical Motors (a division of Emerson Electric Company) entitled "Fundamental Troubleshooting and Problem Analysis."
• The "How to Troubleshoot a Motor" steps listed below will be relevant to future Process Operators, Instrument Technicians, and Mechanic Techs.  However, the content may seem overwhelming at this juncture of PTOA instruction. Therefore … file the information for future reference!
• Your Mentor was not sufficiently amused to learn the dozen "easy steps" which are required to import tables into WordPress from tables that were originally generated using world's most popular software. Ergo there are many large gaps in the below troubleshooting tables.

 

 

"HOW TO TROUBLESHOOT A MOTOR" GUIDELINES:
SYMPTOMS, PROBABLE CAUSES, AND ANALYTICAL STEPS

 

SYMPTOM: THE MOTOR FAILS TO START! 

PROBABLE CAUSE	ANALYSIS
Defective power supply  or Blown or defective primary fuses	Check voltage across all phases above disconnect switch.
Blown or defective secondary fuses	Check voltage below fuses (all phases) with disconnect closed.
Open control circuit  or Overload trips are open	Push reset button.
Defective holding coil in magnetic switch	Push start button and allow sufficient time for operation of time delay (if used). Next check voltage across magnetic holding coil. IF correct voltage is measured THEN the coil is defective. IF no voltage is measured THEN control circuit is open.
Loose or poor connections in control circuits	Make visual inspection of all connections in control switch.
Magnetic switch closes or Poor switch contact	(1)   Open manual disconnect switch. (2)   Close magnetic by hand. (3)   Examine contactors and springs.
Open circuit in control panel	Check voltage at phases T1, T2, and T3.
Open circuit in leads to motor	Check voltage at leads in outlet box.
Leads improperly connected	Check lead numbers and connections.

 

 

 

SYMPTOM: THE MOTOR FAILS TO COME UP TO SPEED! 

Which brilliant PTOA Readers and Students remember learning how to interpret the expected performance of a Centrifugal Pump from the Pump's Performance Curves?

Interpreting Centrifugal Pump expected performance via Performance Curves was featured in PTOA Segments #166, #167, and #168.

Troubleshooting a Centrifugal Pump-Motor combo to rule out or confirm the happenstance of a hydraulic overload will utilized Pump Performance interpretation skills! 

 

PROBABLE CAUSE	ANALYSIS
Low or Incorrect Voltage	Check voltage at phases T1, T2, and T3 in control panel and at motor leads in outlet box.
Incorrect connection at motor	Check for proper lead connections at motor and compare with connection diagram on motor.
Mechanical type overload	Check impeller setting. Check for a tight or locked shaft.
Hydraulic type overload	Check impeller setting. Check GPM with pump capacity and head.

 

 

 

SYMPTOM: THE MOTOR VIBRATES!

The fact is that all Rotating Equipment like Pumps and Motors vibrate.

The challenge for Outside Process Operators is to be aware of the vibration caused by "ambient conditions" and distinguish this environmental vibration from the hint the Pump and Motor are giving that something is really wrong this time.

More modern and more crucial motors will have vibration instrumentation installed which helps determine the magnitude of excessive, non-anticipated Rotating Equipment vibration.   

PROBABLE CAUSE	ANALYSIS
Misaligned Headshaft	Remove top drive coupling and check alignment of motor to pump.
Worn line shaft bearings or Bent line shaft	Disconnect motor from pump and run motor only to determine source of vibration.
Hydraulic disturbance in the discharge piping	Check isolation joint in discharge piping near pump head.
“Ambient Vibration” caused by the environment in which the pump is installed.	When the motor is stopped check the base vibration level.
System Natural Frequency (aka Resonance)	Revise the rigidity of the support structure.

 

 

 

SYMPTOM: THE MOTOR IS TOO NOISY!

The fact is that all industrial sized pumps are also noisy.

PTOA Readers and Students already learned in PTOA Segments #161 and  #164 that the Outside Process Operator must be constantly vigilant to ascertain a  "normal pump noise" from an "abnormal pump noise."

An "abnormal noise" means the pump is trying to warn the Outside Process Operator that something is amiss internally.

The possibility of a worn thrust bearing or anticipated electrical noise upon start up should be investigated prior to pump disassembly.

 

PROBABLE CAUSE	ANALYSIS
Worn thrust bearing.	1.     Remove dust cover. 2.     Rotate rotor by hand while making visual examination of balls and races.   Note: Bearing-generated noise is commonly accompanied by a high frequency vibration and/or increased temperature.
Electrical noise	Most motors are electrically noisy during the starting period. This noise should diminish as the motor reaches full speed.

 

 

 

SYMPTOM: THE  MOTOR IS OVERHEATING!

So … how hot is hot anyway?

Process Operators, Instrumentation Technicians and Mechanic Technicians should never rely on measuring a temperature by their hand!

The temperature of a motor must be measured with a thermocouple (PTOA Segment #107), RTD (PTOA Segment #114) or thermistor (PTOA Segment #116).

The motor in the nearby photo definitely overheated to the point that the windings fused!

Note that the symptom of an overheating motor and an overheating bearing (discussed below) can both be caused by motor overload and/or a plugged motor intake/exhaust.

 

PROBABLE CAUSE	ANALYSIS
Overload	1.     Measure Load and compare to nameplate rating. 2.     Check for excessive friction in motor and if not satisfied check for excessive friction in complete drive. 3.     Still overloaded? You have a choice of reducing the Load OR replacing the motor with a greater capacity motor.
Motor intake or exhaust plugged	Clean motor intake and exhaust areas. Clean filters or screens if motor is equipped with them.
Unbalanced voltage	Check voltage to all phases.
Open stator windings	1.     Disconnect motor from Load. 2.     Check idle amps for balance in all three phases. 3.     Check stator resistance in all three phases.
Over Voltage	Check voltage and compare to nameplate voltage.
Under Voltage	Check voltage and compare to nameplate voltage.
Ground Fault	Locate with test lamp or insulation tester and repair.
Improper Connections	Recheck connections.

 

 

 

SYMPTOM:  A BEARING IS OVERHEATING!

Brilliant PTOA Readers and Students who are reading the PTOA in the intended sequential order learned all about the form and function of Bearings in PTOA Segments #182, #183, and #184 and also learned why Bearings must be lubricated in the PTOA Tribology Focus Study (PTOA Segments #177 through #180).

 

PTOA Readers and Students should notice that the symptom of an overheating motor (discussed above) and an overheating bearing can both be caused by motor overload and/or a plugged motor intake/exhaust.

 

PROBABLE CAUSE	ANALYSIS
Misalignment	Check bearing alignment.
Incorrect lubrication oil	Drain and resupply with correct oil.
Lubrication oil level TOO HIGH or TOO LOW	Verify lubrication oil level is correct.
Excessive thrust	Reduce thrust from the driven machine.
Over-greased Bearing	Relieve bearing cavity of grease to level that was specified by manufacturer.
Motor is overloaded	1.     Measure Load and compare to nameplate rating. 2.     Check for excessive friction in motor and if not satisfied check for excessive friction in complete drive. 3.     Reduce Load or replace motor with greater capacity motor.
Motor intake or exhaust is plugged	Clean motor intake and exhaust areas. Clean filters or screens if motor is equipped with them.

 

 

 

SYMPTOM:  BEARING OIL IS LEAKING AROUND THE DRAIN PLUG!

Wow!

The above troubleshooting steps for an overloaded motor or bearing that is heating up seem complex!

The below troubleshooting steps outline the much more simple  procedure to follow when bearing oil is discovered leaking from the drain plug.

When that happens there is only one plan of attack for the Process Operator and Mechanic Tech to follow!

 

 

PROBABLE CAUSE	ANALYSIS
Insufficient sealant applied to drain plug threads	1.     Remove drain plug. 2.     Drain existing oil from sump. 3.     Wipe excess oil from the plug threads with a clean cloth. 4.     Next clean the threads in the drain hole with the clean cloth. 5.     Apply the manufacturer’s suggested sealant to the threads of the plug and replace the plug. 6.     Fill sump with new oil to the proper level.

 

TROUBLESHOOTING REQUIRES UNDERSTANDING
THE POSSIBLE SOURCES OF THE PROBLEM 

Who amongst the brilliant PTOA Readers and Students noticed that the process of focusing on the  "How to Troubleshoot a Motor" guidelines also connected the dots associated with all the knowledge PTOA Readers and Students have gained while learning about the Centrifugal Pump-Motor Rotating Equipment combo?

Such is the nature with any Troubleshooting guidelines.

Troubleshooting provides a great platform for review because nobody can fix a problem if they are not familiar with the basic form and function of the components and variables that might contribute to the problem.

Next: PTOA Readers and Students will learn about the Rotating Equipment Drivers known as Engines.

 

TAKE HOME MESSAGES: Industrial Rotating Equipment ...  for example a Centrifugal Pump-Motor combo … may exhibit symptoms of pending failure. Prior to dissembling a Motor that is connected to and driving any Load, Process Operators should work with Process Plant Instrument Techs, Electricians, and Maintenance Techs for the purpose of analyzing and troubleshooting Motor problems. 

Common problems include:

• Motors that fail to start.
• Motors that fail to come up to speed.
• Motors that vibrate too much or are noisier than expected.
• Motors that are overheating.
• Bearings that are overheating.
• Bearing oil leaking from drain plugs.

 

The process of troubleshooting provides a great tool to procedurally review the knowledge which has been gained and thence connect the dots between the myriad of potential contributors to the problem. 

WordPress should make it much simpler to import tables that are generated from commonly used popular software.

©2018 PTOA Segment 0190

PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
PTOA PV Pressure Prime Mover/Driver of Rotating Equipment Extension Study
 

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