Larry Bachus, Angel Custodio. Know and Understand Centrifugal Pumps

Bachus Company, Inc., 2003. - 253 p.
Very few industrial pumps come out of service and go into the maintenance shop because the volute casing or impeller split down the middle, or because the shaft fractured into four pieces. The majority of pumps go into the shop because the bearings or the mechanical seal
failed.
Most mechanics spend their time at work time greasing and changing bearings, changing pump packing, and mechanical seals. The mechanical engineers spend their time comparing the various claims of the pump manufacturers, trying desperately to relate the theory learned at the University with the reality of the industrial plant. Purchasing agents have to make costly decisions with inadequate information at their disposal. Process engineers and operators are charged with
maintaining and increasing production.
The focus of industrial plant maintenance has always been that the design is correct, and that the operation of the pumps in the system is as it should be. In this book, you will see that in the majority of occasions, this is not true. Most of us in maintenance spend our valuable time, just changing parts, and in the best of cases, performing preventive maintenance, trying to diminish the time required to change those parts.
This book will help you to step away from the fireman approach, of putting out fires and chasing emergencies. This book is directed toward the understanding of industrial pumps and their systems. It won’t be a guide on how to correctly design pumps, nor how to rebuild and repair pumps. There are existing books and courses directed toward those themes. By understanding the real reasons for pump failure, analyzing those failures, and diagnosing pump behavior through interpretation of pressure gauges, you can achieve. Prologue productive pump operation and contain maintenance costs. This book will serve as a guide to STOP repairing industrial pumps.Prologue
About the Authors
Basic Pump PrinciplesHow do pumps work?
Pressure measurement
Atmospheric pressure (ATM)
Absolute pressure (psia)
Gauge pressure (psig)
Vacuum
Pump head
Specific gravity
Pressure measurement
Pressures inside the pump
NPSH, Net Positive Suction HeadDefinition of NPSHr (required)
Definition NPSHa (available)
CavitationVapor pressure
Cavitation
The effects of vapor pressure on pump performance
Cavitation: A practical discussion
Review for preventing cavitation
Cavitation review
Do something about cavitation
The Affinity LawsThe Laws
The Affinity Laws and the impeller diameter
What’s the practical application of these laws?
Useful Work and Pump Efficiency
Useful work from a pump
Flow determination
Pump efficiency
Factors that affect the efficiency
Calculating pump efficiency
Pump classificationPositive displacement pumps
Centrifugal pumps
Conceptual difference
Centrifugal volute pumps
Types of centrifugal pumps
Overhung impeller
Impeller between the bearings
Turbine pumps
Specific duty pumps
The typical ANSI pump
API (American Petroleum Institute) pumps
Vertical turbine pumps
Non-metallic pumps
Magnetic drive pumps
Canned motor pumps
Pump impellers
Turbine impellers
Conventional impellers
Suction specific speed, Nss
Open impellers
Semi open impeller
Totally enclosed impeller
Wear bands
Specific speed, Ns
Understanding Pump Curves
Pump performance curves
History
Head versus pressure
H-Q
Pump efficiency
The energy (BHp) curve
The pump’s minimum requirements (NPSH)
Special design pumps
Family curves
The System Curve
The system controls the pump
The elements of the Total Dynamic Head (TDH)
Determining the H_s
Determining the H_p
Calculating the H_f and H_v
The dynamic system
Variable elevations
The happy zone
Dynamic pressures
Variable resistances
Short term resistance changes
Long term resistance changes
Pumps in parallel and pumps in series
Pumps in parallel
Three tips
Pumps running in series
Combined parallel and series pump operation
Shaft DeflectionOperation, design and maintenance
Signs of shaft deflection
Interpreting the evidence
The sweet zone
The dual volute pump
Pump and Motor AlignmentTypes of misalignment
Alignment techniques
Equipment alignment sequence
Coupling alignment
BearingsBearing lubrication
Bearing failure
Bearing maintenance
Bearing seals
Pump Shaft Packing
History
Vegetable fibers
Reciprocating action
Packing
Rotary action
Synthetic fibers
Compression packing
The lantern ring
The packing lubricant
Stages in the life of packing
Mechanical Seals
Pump packing
History
The mechanical seal
The single, unbalanced, inside mounted mechanical seal
The single, outside-mounted, unbalanced seal
The single, balanced, internal mechanical seal
The single, balanced, external mechanical seal
Advantages of O-rings
The balance effect
Advantages of balance
Balance explained by math
Cartridge mechanical seals
Double seals
The tandem dual seal
The back-to-back double seal
The face-to-face dual seal
Support systems for dual seals
The thermal convection tank
The turbo tank
The pumping unit
Failure Analysis of Mechanical Seals
Causes of premature seal failure
O-ring (the elastomer) failure
The elastomer sticks to the shaft
The springs clog and jam
The shaft frets under the shaft seal
Incorrect installation dimension
Environmental controls for difficult sealing applications
Difficult pumping applications for mechanical seals
Environmental controls
Proper pump repair alignment methods
Common Sense Failure Analysis
Pump maintenance files
Failure analysis on centrifugal pumps
Why is this pump in the shop?
Avoiding Wear in Centrifugal PumpsErosion
Corrosion
Wear rings
Fluid velocity accelerates wear
Turbulence
Throttling
Pump PipingPiping design to drain tanks and sumps
The Submergence Laws