Gene Vogel
EASA Pump & Vibration Specialist

This technical paper was presented at the 2014 EASA Convention.

The impeller is generally the most difficult pump component to repair and the most expensive to replace. This paper looks at case histories of failed pumps and the steps to determine the cause of failure.

• Erosion, corrosion, cavitation or wear. What happened to this impeller?
• How to spot the tell-tale signs
• What operational conditions led to impeller damage

Gene Vogel
EASA Pump & Vibration Specialist

When repairing centrifugal and axial flow pumps, axial thrust is a concern. An understanding of the causes and the mitigating provisions of various pump designs will help repair technicians to ensure those provisions work properly. Various impeller designs, end suction and vertical turbine pumps will be a primary focus. 

Primary topics are: 

• Factors affecting the amount of axial thrust developed by an impeller 
• Review of some common mitigation designs 
• What repair technicians need to look for on various pump designs 

The mechanical pump components can be repaired without understanding the hydraulics of how a pump works. But it’s easy to miss important features that can affect pump performance and reliability.  

This presentation will be helpful for pump repair technicians and supervisor and engineers associated with pump repair.

Gene Vogel
Especialiste de Bombas y Vibraciones

Al igual que con la mayoría de las otras máquinas reparadas comúnmente en los centros de servicio de EASA, el balanceo dinámico de los impulsores de las bombas es una cuestión importante. El desbalanceo excesivo imparte fuerzas sobre los rodamientos, reduciendo su vida útil y sometiendo los soportes de las máquinas a una energía vibratoria que deteriora las fundaciones.

Desde la perspectiva del balanceo dinámico, los rotores de las bombas difieren mucho de los de los motores eléctricos más populares. La masa del rotor de un motor eléctrico se encuentra entre los rodamientos y la longitud de los rotores exceden a sus diámetros. Muchos impulsores de las bombas se encuentran montados en voladizo y es probable que sean más angostos que sus diámetros. Los componentes angostos pueden requerir reglas especiales para asignar el desbalanceo residual permisible (según ISO 21940-11), y pueden ser necesarias técnicas especiales para un balanceo eficiente en la máquina balanceadora.

Gene Vogel
Especialista de Bombas & Vibraciones de EASA

Es común encontrar impulsores de bombas con daños significativos en la superficie. Las tres causas más comunes de daño superficial son la erosión, la corrosión y la cavitación. En cada uno de estos problemas existen características que ayudarán a indicar la causa primaria de fallo por lo que será útil una breve descripción de cada uno de estos tres fenómenos. La erosión es la más sencilla; esta simplemente es el desgaste de las superficies del impulsor ocasionada por los materiales abrasivos suspendidos en el bombeo. La corrosión también es simple ya que es una reacción química entre las moléculas ionizadas en el bombeo y los elementos metálicos del impulsor. La oxidación es la corrosión más común en los impulsores de las bombas. La cavitación es un fenómeno más complejo y tiene que ver con la formación e implosión de burbujas en el bombeo debido a los cambios de presión presentes cuando el bombeo fluye a través del impulsor. La baja presión en la succión permite que se formen burbujas de vapor y luego estas burbujas implosionan a medida que aumenta la presión a través del impulsor. La apariencia del daño en las superficies del impulsor refleja las características de cada uno de estos tres fenómenos.

Gene Vogel
EASA Pump & Vibration Specialist

It’s common to find pump impellers with significant surface damage. The three most common causes of surface damage are erosion, corrosion and cavitation. For each of these there are characteristics which will help indicate the primary cause of the damage.

A brief description of each of the three phenomenon will be helpful:

• Erosion is the simplest; it is simply the wear to the impeller surfaces from abrasive materials suspended in the pumpage.
• Corrosion is also straightforward; corrosion is a chemical reaction between ionized molecules in the pumpage and metallic elements of the impeller. Oxidation is the most common corrosion on pump impellers.
• Cavitation is a more complex phenomenon. Cavitation is all about bubbles forming and imploding in the pumpage due to the pressure changes that occur as the pumpage flows through the impeller. Low pressure at the suction allows vapor bubbles to form and then these bubbles implode as the pressure increases through the impeller.

The appearance of the damage to the impeller surfaces reflects the characteristics of the each of these three phenomenon.

Gene Vogel
EASA Pump & Vibration Specialist

Whether it is a simple re-application of a pump from 50 Hz to 60 Hz (or vice versa), the repurposing of an existing pump, or the application of a new pump to an existing application, determining the proper trim for an impeller can be challenging. This presentation reviews: 

• Basic impeller design criteria 
• Methods of evaluating the head and flow and power implications of trimming impeller outside diameters

This recording will benefit pump technicians, engineers and sales personnel.

Gene Vogel
EASA Pump & Vibration Specialist

As with most other machines commonly repaired in EASA service centers, dynamic balancing on pump impellers is an important concern. Excessive imbalance imparts forces on bearings, reducing their lives and subjecting machine mountings to vibratory energy that deteriorates foundations.

Pump rotors are quite different than more familiar electric motor rotors from a dynamic balance perspective. The mass of an electric motor rotor is between the bearings, and the rotors are longer than their diameters. Many pump impellers are mounted in an overhung configuration, and the impellers will likely be narrower than their diameters. Narrow components may require special rules for allocating allowable residual imbalance (per ISO 21940-11), and special balancing techniques may be needed for efficient balancing in the balancing machine.

The repair of the various types of pumps represents an important segment of the service center repair market. Electric motors and pumps are the two most widely used industrial machine components.

Although there are two principle pump types (dynamic and positive displacement), this manual focuses on dynamic pumps and the fundamentals of dynamic pump repair. The information it contains will be helpful to both novice and experienced pump repair technicians, to supervisors and managers of pump repair operations, and to customer service and sales personnel who communicate with customers about pump repair issues.

Section 2 covers repair concerns and techniques common to most pumps, while the following sections focus on specific pump types and the unique concerns associated with repairing them. These sections include submersible pumps, vertical turbine pumps, end suction pumps and split case pumps. Where appropriate, these sections may reference the general repair information in Section 2.

Table of Contents- (Download the complete Table of Contents)

1. Nomenclature
2. General Pump Repair Procedures
3. Submersible Pumps
4. Vertical Turbine Pumps
5. End Suction Radial Split Pumps
6. Axial Split-Case Pumps
7. Seals
8. Pump Reliability
9. Glossary and Standards Organizations

8 presentations

$40 for EASA members

 

A special discounted collection of 8 webinar recordings focusing on various aspects of pump repair.

Once purchased, all 8 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

Troubleshooting Pump Performance Problems
Presented May 2017

This presentation covers:

• Not enough pressure (head) or not enough flow – how do you respond?
• How to determine if a pump is operating properly
• Differentiating a pump problem from a system problem
• Determining pump load and power requirements
• The effect of fluid parameters and cavitation on pump performance. 

Target audience: This will be most useful for service center technicians and engineers. The content will also be beneficial for supervisors and managers who are responsible for pump failure analysis and testing. 

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Pump Failure Case Study
Presented December 2013

This presentation covers:

• Brief overview of disassembly and evidence of failure
• Discussion of possible failure scenarios
• Review of actual repairs, modification and reassembly
• Update of machine's present operation

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Repair Tips for Submersible Pumps
Presented February 2013

This presentation focuses on:

• Types of submersible pumps
• Tips on seal arrangements
• Common repair procedures
• Cables and cable entries
• Testing submersibles in the service center

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Assessing Impeller Damage
Presented May 2019

The impeller is generally the most difficult pump component to repair and the most expensive to replace. This session will look at case histories of failed pumps and the steps to determine the cause of failure. Topics covered include:

• Erosion, corrosion, cavitation or wear: What happened to this impeller?
• How to spot the tell-tale signs
• What operational conditions led to impeller damage

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Repairing Impeller Damage
Presented May 2016

We’ve covered how to assess impeller damage. Now learn how to fix that damage. This presentation covers: 

• Replacing/repairing wear rings
• Repairing cavitation damage
• Impeller replacement options
• Dynamic balancing impellers

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Techniques for Straightening Pump Shafts
Presented March 2011

The slender dimensions of many pump shafts make them susceptible to distortion, which affects pump performance and reliability. This recording presents a methodical approach and effective techniques for measuring and correcting shafts which are bent or twisted.

Target audience: This presentation is intended for service center supervisors, managers and machine shop technicians.

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Vertical Turbine Pump Repair Tips
Presented February 2012

Vertical turbine pumps are used extensively in every segment of industry. Although they are not complex, repairing them in the service center can present a few challenges. This presentation gives some approaches and procedures that experience has shown will make the job easier.

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Final Testing for Pumps - An Overview
Presented November 2014

The pump repairs are completed! Now the pump needs to be tested. This presentation discusses the procedures for the basic tests that can be performed on pumps that have been repaired in the service center.

Final testing of pumps can include:

• Operational tests
• Seal leakage test
• Motor chamber leakage test (submersibles)
• Casing pressure test

While some of these tests are not difficult to perform, knowing the methods and limits will help service centers to confidently deliver quality pump repairs.

Gene Vogel
EASA Pump & Vibration Specialist

Corrosion and/or erosion damage is inevitable for some pump applications. Pumps received for repair with significant damage may look like a candidate for the junk bin, but with proper repair techniques can often be restored to original performance – or perhaps better than original. Damage from corrosion and erosion (henceforth “damage”) can occur on stationary pump components as well as on the rotating impeller. Note: Cavitation damage is a form of erosion damage.

Gene Vogel
Especialista de Bombas & Vibraciones de EASA

En algunas aplicaciones, los daños por corrosión y/o erosión de las bombas son inevitables. Las bombas enviadas para reparación que presentan daños significativos pueden parecer buenas candidatas para ser desechadas, pero a menudo con las técnicas de reparación adecuadas pueden restaurarse a sus condiciones originales o quizás a unas mejores. Los daños por corrosión y erosión (en adelante “daño”) se pueden presentar en las partes estáticas de las bombas, así como también en el impulsor rotativo. Nota: La cavitación es una forma de daño por erosión.

Gene Vogel
EASA Pump & Vibration Specialist

Centrifugal pump failures are most commonly attributed to seal failure, impeller damage and bearing failures. A good understanding of failure modes for seals, impellers and bearings is essential to providing customers with reliable pump repairs. This presentation will explore various failure modes and provide some direction on ways to avoid them.  

• How mechanical pump seals operate, the importance of seal face material selection and proper installation techniques 
• Impeller damage examples and causes 
• General rolling element bearing failure modes 
• Bearing failure modes unique to vertical turbine pumps and associated vertical motors 

This recording will be useful for service center engineers, pump technicians and operations managers.