Centrifugal Pump
A centrifugal pump is a mechanical device that uses a rotating impeller to increase the pressure of a fluid. It works by converting the rotational kinetic energy of the impeller into hydrodynamic energy in the fluid. This type of pump is commonly used in industrial, agricultural, and municipal applications for moving liquids.
8 Key excerpts on "Centrifugal Pump"
eBook - ePubPump Wisdom
Essential Centrifugal Pump Knowledge for Operators and Specialists
- Robert X. Perez, Heinz P. Bloch(Authors)
- 2021(Publication Date)
- Wiley-AIChE(Publisher)
...1 Principles of Centrifugal Process Pumps Pumps, of course, are simple machines that lift, transfer, or otherwise move fluid from one place to another. They are usually configured to use the rotational (kinetic) energy from an impeller to impart motion to a fluid. The impeller is located on a shaft; together, shaft and impeller(s) make up the rotor. This rotor is surrounded by a casing; located in this casing (or pump case) are one or more stationary passageways that direct the fluid to a discharge nozzle. Impeller and casing are the main components of the hydraulic assembly ; the region or envelope containing bearings and seals is called the mechanical assembly or power end (Figure 1.1). Many process pumps are designed and constructed to facilitate field repair. On these so‐called “back pull‐out” pumps, shop maintenance can be performed, while the casing and its associated suction and discharge piping (Figure 1.2) are left undisturbed. Although operating in the hydraulic end, the impeller remains with the power end during removal from the field. The rotating impeller (Figure 1.3) is usually constructed with swept‐back vanes, and the fluid is accelerated from the rotating impeller to the stationary passages into the surrounding casing. In this manner, kinetic energy is added to the fluid stream (also called pumpage) as it enters the impeller's suction eye (A on Figure 1.3), travels through the impeller, and is then flung outward toward the impeller's periphery. After the fluid exits the impeller, it gradually decelerates to a much lower velocity in the stationary casing, called a volute casing, where the fluid stream's kinetic energy is converted into pressure energy (also called pressure head)...
- Amithirigala Widhanelage Jayawardena(Author)
- 2021(Publication Date)
- CRC Press(Publisher)
...In steam turbines, it is the steam pressure produced by heat. In gas turbine, it is the gas pressure produced by chemical energy. 12.4 Centrifugal Pump The flow in a Centrifugal Pump is radially outwards. They are so called because the centrifugal force or the variation of pressure due to rotation is an important factor in their operation. A rotating impeller provides the energy to the fluid in the form of a velocity head which is converted into a pressure head as the fluid leaves the pump. There is a pronounced change in the radius from inlet to outlet. Centrifugal Pumps operate efficiently for water and other liquids with low viscosity. They are not suitable for high-viscosity fluids and high pressure. Multi-stage pumps can be used to deliver high pressure. A Centrifugal Pump consists of an impeller rotating inside a casing. There are centrifugal turbines, pumps and compressors. The flow is usually towards the larger radius for a pump and radially inwards for a turbine. Centrifugal Pumps are broadly divided into two classes; namely, the diffuser type and the volute type. A diffuser type pump is one in which the impeller is surrounded by a diffuser containing stationary guide vanes. There is a lowering of kinetic energy and, therefore, an increase of pressure energy. Volute type pumps do not have diffuser vanes, but instead, have diverging spiral casings so proportioned to reduce the velocity of flow and to convert some of the velocity head to static pressure head. The spiral is called the volute. The rotating impeller converts the mechanical energy to kinetic energy and the volute, or the diffuser then converts some of the kinetic energy to pressure energy. The faster and larger the impeller, the greater the amount of energy transferred to the fluid. The diffuser type is more bulky and expensive. But the gain in efficiency is about 80% compared with 75%–80% for volute type...
- Ron Palgrave(Author)
- 2019(Publication Date)
- Butterworth-Heinemann(Publisher)
...These are known as Mixed Flow or diagonal flow pumps. The term Centrifugal Pump strictly relates to the first group only, those where the flow leaves radially. In these cases, centrifugal forces are by far the dominant contributor to the way in which pump pressure head is created. But this is not the only contributor. At the other extreme, in cases where the liquid leaves the impeller axially, it does so at the same radial distance from the shaft as when it entered. With no change of radius, there can be no obvious centrifugal force. Instead the pressure head is generated almost entirely by a different mechanism. In the case of mixed flow pumps, the contributions from both mechanisms might be comparable. In fact, most practical members of this part of the pump family generate head from combinations of these two mechanisms. However, the term Centrifugal Pump has come to describe any member of the family (Fig. 3.1). The main purpose of almost every Centrifugal Pump is to create flow in a liquid system. To do so they have to simultaneously generate pressure head in the liquid. This pressure head is then dissipated by the liquid system resistance while handling the above-mentioned flow. Though the pump still has to generate pressure head as a by-product, its chief purpose is to create a specified system flow. On very rare occasions, Centrifugal Pumps are installed for the main purpose of creating hydrostatic pressure. But generally, other classes of pumping machine are better suited to this aim. Fig. 3.1 The general appearance of rotodynamic pump impellers. Compared to many other machines, the inner workings of a Centrifugal Pump are largely invisible, except in certain laboratory research pumps. This means that the underlying physics are less than obvious. The detail physics of the liquid flow path are well covered elsewhere [3, 33], but at a level inappropriate to this volume. Therefore, a simpler description is given here...
- Paul N. Cheremisinoff(Author)
- 2019(Publication Date)
- Routledge(Publisher)
...18 Pumps INTRODUCTION Transporting liquids to and from process equipment is an integral part of water treatment and distribution technology. Energy requirements depend on the height through which the fluid is mixed, the length and diameter of the transporting conduits, the rate of flow, and the fluid’s physical properties (in particular, viscosity and density). In some applications, external energy for transferring fluids is not required. For example, when liquid flows to a lower elevation under the influence of gravity, a partial transformation of the fluid’s potential energy into kinetic energy occurs. When transporting fluids through horizontal conduits, especially to higher elevations within a system, mechanical devices such as pumps are employed. Methods for transporting fluids between process equipment include • Centrifugal force inducing fluid motion • Volumetric displacement of fluids, either mechanically or with other fluids • Mechanical impulse • Transfer of momentum from another fluid • Electromagnetic forces • Gravity induced The first four methods are described in this chapter and emphasis is placed on mechanical devices for transporting incompressible fluids, namely, pumps. CLASSIFICATIONS AND CHARACTERISTICS Major types of pumps used in process plant applications are centrifugal, axial, regenerative turbine, reciprocating, metering, and rotary. These classes are grouped under one of two categories: dynamic pumps or positive displacement pumps. Dynamic pumps include centrifugal and axial types and are operated by developing a high liquid velocity, which is converted to pressure in a diffusing flow passage. These pumps generally are lower in efficiency than the positive displacement types. However, they do operate at relatively high speeds, thus providing high flowrates in relation to the physical size of the pump...
eBook - ePub- Barbara Hauser(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...Chapter 12 Centrifugal Pumps I Man has always needed to move water from one place to another against the forces of nature. Gravity will move it downhill on a grade. If depth is built up behind, that pressure will move it further. But when pressure is dissipated by friction loss, when water in the valley is needed on the mountain, the energy to move that water must be created. A pump is needed. Archimedes invented the screw pump in 287 BC. It physically lifts volumes of liquid, but has space and height limitations. It is said that the Roman emperor, Nero invented the piston pump at about 100 AD. Volume after volume of water is displaced with each stroke, but this is a high energy consumer, and size limits capacity. Pumping technology was restricted to these, and variations, until the nineteenth century. Th e basic concept of the Centrifugal Pump existed during the 1600’s, but development was slow because the high speed drives needed were not available for another 200 years. It wasn’t until the 1800’s that the first fully functional Centrifugal Pumps were developed. These can move great volumes of water with much smaller units than the pumps previously in use. Centrifugal Pumps operate with high efficiency, few parts are required, initial cost is low, and maintenance is relatively easy. Operation of the Centrifugal Pump is based on the principle that a high velocity is imparted to the water as it enters the pump, and that velocity is converted to pressure as the water exits the pump. From a mechanical standpoint, water enters through the center, or “eye”, of a rapidly rotating impeller. It is moved through the impeller vanes and thrown off their tips with great velocity. Still contained by the pump casing, the water cannot escape the unit, and collects at the “volute”, or exit, slowing down as it leaves the pump. From a hydraulic standpoint, note the energy changes that occur in the moving liquid. As water enters the pump from the suction piping, pressure is low...
eBook - ePub- Sulzer Sulzer Pumps(Author)
- 2010(Publication Date)
- Butterworth-Heinemann(Publisher)
...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 = R ω, 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 β 2 than with the actual flow c 2u, which is not vane-congruent (see Fig. 1.1)...
- Barbara Renner(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...CHAPTER 12 Centrifugal Pumps 12.01 The number and variety of Centrifugal Pumps in water or wastewater treatment plants that have to be maintained are infinite in number. They vary from simple sump pumps to multistage booster pumps powered by motors of several hundred horsepower. Although each style has its own individual construction characteristics, all pumps have the same basic individual parts. Included are shafts, impellers, and casings. They also have bearings, packings, and seals. These parts were discussed in detail in previous chapters. 12.02 The majority of pump maintenance is directed to bearings, packings, and seals. However, pump maintenance extends beyond the obvious mechanical components. Although a pump may appear to be running satisfactorily, there may be internal problems, such as corrosion or erosion, which are occurring that cannot be seen and do not cause any vibration or noise. These problems are detected during routine pump maintenance when the pump is opened for repairs or inspection. 12.03 Sometimes, a pump may not perform properly. Often, these problems are not a result of mechanical component failures but are related more to the condition of valves or other components in the piping system (Table 12.1). When a pump fails to deliver water as it did when it was first installed, the basic system components should be checked. Make sure that everything is set up and functioning properly so the pump can receive water and deliver it to the system. SYSTEM HYDRAULICS 12.04 The hydraulic condition of the system has a direct effect on pump operation. It is, therefore, important to understand system hydraulics when trying to analyze pump problems. Understanding the hydraulics associated with Centrifugal Pumps is not a complicated subject that requires a degree in engineering...
- Mei Zu-yan(Author)
- 2018(Publication Date)
- Routledge(Publisher)
...Chapter 12 Construction of Centrifugal Pumps Huang Jing-Guo 12.1 General Trends of Impeller Design The Centrifugal Pump is the most widely used type of all rotodynamic pumps today. The name centrifugal originated from the very early days of pump history. Judging from the direction of flow through the pump, radial-flow would be more fitting for this type as compared with other types of pumps described in this volume. When analysed from concepts of fluid motion, centrifugal force is not the only force exerting on the fluid in such a pump, nor are the other types of pumps free from centrifugal forces. However, as the name Centrifugal Pump is so predominantly used in the industry today, this more conventional name is retained in the text of this chapter. 12.1.1 Specific speed The specific speed represents a similarity criterion for ail rotodynamic pumps. When two impellers are geometrically and dynamically similar, they will have the same specific speed. The specific speed is the condition of similitude for enlarging or reducing a known impeller design. From dimensional analysis, the expression is designated specific speed, where speed n is in min −1 ; flow rate Q in m 3 s −1 ; and head H in m. In most European countries, the specific speed is expressed as Obviously, there Is the relation n s = 3.65 n q. The numerical value of the specific speed, will vary greatly with different definition formula and different units used. The following table shows the conversion constants between a number of commonly used expressions. Table 12.1 Conversion constants for specific speed expressions It should be pointed out that impellers of the same specific speed may differ in geometric shape because of different hydraulic considerations assumed in the designs...
