Centrifugal Pump Handbook

Sulzer Sulzer Pumps, Sulzer Pumps

• Publisher: Butterworth-Heinemann
• Year: 2010
• eBook ISBN: 9780080942650
• Edition: 3
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

This long-awaited new edition is the complete reference for engineers and designers working on pump design and development or using centrifugal pumps in the field. This authoritative guide has been developed with access to the technical expertise of the leading centrifugal pump developer, Sulzer Pumps. In addition to providing the most comprehensive centrifugal pump theory and design reference with detailed material on cavitation, erosion, selection of materials, rotor vibration behavior and forces acting on pumps, the handbook also covers key pumping applications topics and operational issues, including operating performance in various types of circuitry, drives and acceptance testing. - Enables readers to understand, specify and utilise centrifugal pumps more effectively, drawing on the industry-leading experience of Sulzer Pumps, one of the world's major centrifugal pump developers - Covers theory, design and operation, with an emphasis on providing first class quality and efficiency solutions for high capital outlay pump plant users - Updated to cover the latest design and technology developments, including applications, test and reliability procedures, cavitation, erosion, selection of materials, rotor vibration behaviour and operating performance in various types of circuitry

Chapter one Physical Principles

1.1 Energy Conversion in Centrifugal Pumps

In contrast to displacement pumps, which generate pressure hydrostatically, energy is converted in centrifugal pumps by hydrodynamic means. A one-dimensional representation of the complex flow patterns in the impeller allows the energy transfer in the impeller to be computed from the fluid flow momentum theorem (Euler equation) with the aid of vector diagrams as follows (Fig. 1.1):

Figure 1.1 Vector diagrams

The torque acting on the impeller is defined as:

(1)

With u = Rω, the energy transferred to the fluid from the impeller is defined as:

(2)

The power transferred per unit mass flow to the fluid being pumped is defined as the specific work Y_LA done by the impeller. This is derived from equation (2) as:

(3)

The useful specific work Y delivered by the pump is less than that done by the impeller because of the losses in the intake, impeller and diffuser.

These losses are expressed in terms of hydraulic efficiency η_h:

(4)

The specific work done thus depends only on the size and shape of the hydraulic components of the pump, the flow rate and the peripheral velocity. It is independent of the medium being pumped and of gravitational acceleration. Therefore any given pump will transfer the same amount of energy to completely different media such as air, water or mercury.

In order to use equation (4) to calculate the specific work done by the pump, the flow deflection characteristics of the impeller and all the flow losses must be known. However, these data can only be determined with sufficient precision by means of tests.

In all the above equations the actual velocities must be substituted.

If it were possible for the flow to follow the impeller vane contours precisely, a larger absolute tangential flow component c_2u∞ would be obtained for a given impeller vane exit angle β₂ than with the actual flow c_2u, which is not vane-congruent (see Fig. 1.1). The difference between c_2u∞ and c_2u is known as “slip”. However, slip is not a loss that causes any increase in the pump’s power consumption.

In order to examine the interrelationship between a pump and the pumping plant in which it is installed (Fig. 1.2), it is necessary to consider the energy equation (Bernoulli equation). In terms of energy per unit mass of pumped fluid it can be written:

Figure 1.2 Pumping plant

(5)

1.2 Power, Losses and Efficiency

Equations (1) to (4) hold only as long as no part load recirculation occurs. The same assumption is implied below.

The impeller flow Q_LA generally comprises three components:

• • the useful flow rate (at the pump discharge nozzle): Q;
• • the leakage flow rate (through the impeller sealing rings): Q_L;
• • the balancing flow rate (for balancing axial thrust): Q_E.

Taking into account the hydraulic losses in accordance with equation (4), the power transferred to the fluid by the impeller is defined as:

(6)

The power input required at the pump drive shaft is larger than P_LA because the following losses also have to be taken into account:

• • disc friction losses P_RR (impeller side discs, seals);
• • mechanical losses P_m (bearings, seals);
• • frictional losses P_ER in the balancing device (disc or piston).

The power input required at the pump drive shaft is calculated from:

(7)

If the volumetric efficiency η_v is:

(8)

the power input required by the pump can be written as:

(9)

Pump efficiency is defined as the ratio of ...

Table of contents

• Cover
• Title Page
• Copyright
• Table of Contents
• Preface
• Chapter One: Physical Principles
• Chapter Two: Behavior of Centrifugal Pumps in Operation
• Chapter Three: Acceptance Tests with Centrifugal Pumps
• Chapter Four: Special Data for Planning Centrifugal Pump Installations
• Chapter Five: Mechanical Components
• Chapter Six: Pipelines, Valves and Flanges
• Chapter Seven: Centrifugal Pump Drives
• Chapter Eight: Materials and Corrosion
• Chapter Nine: Principal Features of Centrifugal Pumps for Selected Applications
• Index