INTRODUCTION
A pump is a machine that imparts energy into a liquid to lift the liquid to a higher level, to transport the liquid from one place to another, to pressurize the liquid for some useful purpose, or to circulate the liquid in a piping system by overcoming the frictional resistance of the piping system. The pump is one of the oldest machines invented by man. The earliest pumps devised for raising water, such as the Persian and Roman waterwheels and the more advanced Archimedes screw, were invented to raise water from the hold of a ship. Since that time, many variations and applications of pumps have been developed, which in most cases can be classified into two basic methods used to impart energy to a liquid: volumetric or positive displacement, and addition of kinetic energy.
Volumetric (positive) displace meant of a fluid can be accomplished either mechanically by the action of a screw or a plunger, or by the use of another fluid. Kinetic energy can be added to a fluid by rotating the fluid at high speeds, in a device typically known as a centrifugal pump, or by providing an impulse in the direction of flow. Because of the many and varied uses and applications for a pump, it is easy to understand why so many types of pumps have evolved, as shown in Fig. This chapter focuses on pumps in power station applications and those characterized as kinetic, or more commonly known as centrifugal pumps. This narrowing of the focus permits a more detailed examination of power station pump applications and their associated pumping systems, and therefore positive displacement type pumps are not discussed further here. A good starting source for a basic understanding of these pumps is the Hydraulic Institute Standards. illustrates some of the typical power station pump applications and the type of pump commonly used in each application. A pump is a machine that imparts energy into a liquid to lift the liquid to a higher level, to transport the liquid from one place to another, to pressurize the liquid for some useful purpose, or to circulate the liquid in a piping system by overcoming the frictional resistance of the piping system. The pump is one of the oldest machines invented by man. The earliest pumps devised for raising water, such as the Persian and Roman waterwheels and the more advanced Archimedes screw, were invented to raise water from the hold of a ship. Since that time, many variations and applications of pumps have been developed, which in most cases can be classified into two basic methods used to impart energy to a liquid: volumetric or positive displacement, and addition of kinetic energy.
KINETIC PUMP TYPES AND CHARACTERISTICS
Kinetic pumps can be divided into two classes: centrifugal and regenerative. As listed the most common type of kinetic pump used in a modern central power plant is the centrifugal pump. Although the first centrifugal pump was developed in the late 1600s, most of the development of this pump type has occurred in the present century. Centrifugal pumps include radial, axial, and mixed flow types, with the radial flow volute type used for the bulk of power plant applications. Regenerative pumps are typically referred to as vortex, peripheral, or turbine pumps.
Kinetic pumps can be divided into two classes: centrifugal and regenerative. As listed the most common type of kinetic pump used in a modern central power plant is the centrifugal pump. Although the first centrifugal pump was developed in the late 1600s, most of the development of this pump type has occurred in the present century. Centrifugal pumps include radial, axial, and mixed flow types, with the radial flow volute type used for the bulk of power plant applications. Regenerative pumps are typically referred to as vortex, peripheral, or turbine pumps.
Volute Type Centrifugal Pumps
The operating principle of a volute pump is shown in Fig.
The operating principle of a volute pump is shown in Fig.
Liquid enters the pump at the impeller eye and is thrown radially outward through an expanding pump casing. This action creates a low pressure at the impeller eye which draws more liquid into the impeller. The velocity head imparted to the liquid by the impeller is converted into static pressure by the widening spiral pump casing.
Diffuser Type Centrifugal Pumps
Another type of radial flow centrifugal pump is the diffuser pump, shown in Fig. 11-3. As with the volute centrifugal pump, the liquid enters a diffuser type pump at the impeller eye and is thrown outward along the impeller vanes. After the liquid has left the impeller, it is passed through a ring of stationary guide vanes that surround the impeller and diffuse the liquid to provide a controlled flow and efficient conversion of velocity head into static pressure.
Another type of radial flow centrifugal pump is the diffuser pump, shown in Fig. 11-3. As with the volute centrifugal pump, the liquid enters a diffuser type pump at the impeller eye and is thrown outward along the impeller vanes. After the liquid has left the impeller, it is passed through a ring of stationary guide vanes that surround the impeller and diffuse the liquid to provide a controlled flow and efficient conversion of velocity head into static pressure.
Axial Flow and Mixed Flow Centrifugal Pumps In an axial flow pump, the impeller acts as a propeller. Liquid flows parallel to the axis or shaft of the pump, as shown in Fig. Pressure is generated by the propelling and lifting action of the impeller vanes on the liquid. Normally, diffusion vanes are located on the discharge side of the pump to eliminate rotation and radial velocity of the liquid imparted by the impeller. In mixed flow pumps, liquid is discharged both radially and axially into a volute type of casing. Pressure is developed both by centrifugal force and by the lift of the impeller vanes on the liquid. The action of a mixed flow impeller is shown in Fig.
Regenerative Pumps
A regenerative type of centrifugal pump has an impeller with vanes on both sides of a rim that rotates in a channel in the pump's casing, as shown in Fig.
A regenerative type of centrifugal pump has an impeller with vanes on both sides of a rim that rotates in a channel in the pump's casing, as shown in Fig.
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