Technology & Engineering
Fluid Pumps
Fluid pumps are devices used to move liquids or gases by increasing the fluid's pressure. They are commonly used in various applications, including industrial, commercial, and residential settings. Fluid pumps come in different types, such as centrifugal pumps, positive displacement pumps, and axial flow pumps, each designed for specific fluid-handling needs.
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- Paul N. Cheremisinoff(Author)
- 2019(Publication Date)
- Routledge(Publisher)
18 Pumps INTRODUCTIONTransporting 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 CHARACTERISTICSMajor 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. Furthermore, they usually have significantly lower maintenance requirements than positive displacement pumps.
eBook - ePub- DENNIS A SNOW(Author)
- 2001(Publication Date)
- Butterworth-Heinemann(Publisher)
20Pumps and pumping
Keith Turton, BSc(Eng), CEng, MIMechE, Visiting Fellow, School of Mechanical Engineering Cranfield UniversityContentsPump functions and dutiesPump principlesRotodynamic pumps Scaling laws and specific speed Positive displacement pump principlesEffects of fluid properties on pump behaviourFlow losses in systemsFriction losses Losses in bends, valves and other features Presentation of system lossInteraction of pump and systemSteady-state matching of pump and system Flow control Multiple-pump layouts Suction systemsCavitationNet positive suction head (NPSH)Priming systemsSeals: selection and careCentrifugal pump and rotary pump seal systems Reciprocating pump seal systemsPump and drive selectionPump selection Drive selection The economics of pump selection and running maintenance Reliability considerationsPump testingFactory tests Scale-model testing20.1 Pump functions and duties
Pumps impart energy to the liquids being transferred by mechanical means using moving parts. They can be classified as rotodynamic or positive displacement. Rotodynamic pumps cause continuous flow, and the flow rate and discharge pressure are effectively constant with time. Positive displacement pumps deliver fixed quantities at a rate determined by driving speed. The main types of pump commonly used are listed in Figure 20.1 .Figure 20.1 Pump family treesPumps are used to transfer liquids, moving blood and other biological fluids, delivering measured quantities of chemicals as in dosing in water treatment, in firefighting, in irrigation, moving foods and beverages, pumping pharmaceutical and toilet products, in sewage systems, in solids transport, in water supply and in petrochemical and chemical plant. They are utilized in power transfer, braking systems, servomechanisms and control, as well as for site drainage, water-jet cutting, cleaning and descaling. Pumps thus give a wide range of pressure rises and flow rates with pumping liquids which vary widely in viscosity and constituency.
- Amithirigala Widhanelage Jayawardena(Author)
- 2021(Publication Date)
- CRC Press(Publisher)
Chapter 12 Fluid machinery12.1 Introduction
Fluid machinery can be broadly classified into two types; namely, pumps and turbines. Pumps convert mechanical energy into fluid energy, thereby increasing the energy of the fluid (increase of pressure). Turbines convert the fluid energy into mechanical energy, thereby decreasing the energy of the fluid.Compressor is also a pump. Its primary function is to increase the pressure of the gas. Fan and Blower are machines used only for causing the movement of gas.12.2 Types of pumps
There are various types of pumps; some have only historical importance. Examples include.12.2.1 Chain or bucket pumps
This is the simplest type of pump that uses gravity lift. It has a valve which opens when it goes below the water line and closes when lifted above the water line.12.2.2 Static or positive displacement pumps
Positive displacement type functions by changes of the volume occupied by the fluid within the machine. They create an expanding cavity on the suction side and a contracting cavity on the delivery side. The operation of a positive displacement type machine depends only on mechanical and hydrostatic principles. Only a few principles of fluid dynamics are involved. Positive displacement pumps are more suitable for low flow high-pressure situations, and their efficiency is relatively independent of the pressure. They are preferred for moving viscous fluids such as oil, asphalt, etc. There are several types of positive displacement pumps.12.2.2.1 Reciprocating type
They are usually of piston−cylinder combination with inlet and exit valves involving suction and compression. Work done by pump is ∫pdv
eBook - ePubEnvironmental Engineering
Fundamentals and Applications
- Subhash Verma, Varinder S. Kanwar, Siby John(Authors)
- 2022(Publication Date)
- CRC Press(Publisher)
15 Pumps and Pumping DOI: 10.1201/9781003231264-15In water distribution, a wide variety of pumps are used to transport water. Though centrifugal pumps are common, other types of pumps are also used in special applications. The two broad categories of pumps are positive displacement pumps and kinetic or velocity pumps.15.1 Positive Displacement Pumps
These pumps are designed to deliver a fixed quantity of fluid for each revolution of the pump rotor. Therefore, except for minor slippage, the delivery of the pump is unaffected by changes in the delivery pressure. In general, these pumps will pump against high pressure, but their capacity is low. These pumps are well-suited for pumping high viscosity liquids and can be used for metering since output is directly proportional to rotational speed. Reciprocation pumps, piston pumps and rotatory pumps are all examples of positive displacement pumps.15.2 Velocity Pumps
As the name indicates, this category of pump adds to the kinetic energy of the fluid, which is later converted to pressure energy. A centrifugal pump is the most commonly used velocity pump. Non-positive displacement pumps are generally used to transfer large volumes of liquids at relatively low pressures. However, if pressure is increased, pumping rate drops. This is in strong contrast with positive displacement pumps.15.2.1 Types of Centrifugal Pumps
A centrifugal pump has a radial flow or mixed type impeller. The casing of a centrifugal pump may be either volute type or turbine type, also called diffuser casing. In a volute pump, flow velocity is reduced as the water enters the outlet, thus increasing the pressure. In a turbine pump, velocity is reduced by stationary guide vanes before the water enters the casing, thus giving a better transfer of flow energy or efficiency.Turbine Pumps
Turbine pumps are usually multistage and used for pumping from deep wells. In multistage pumps, each stage adds the same head. The prime mover is kept at ground surface level and impellers are attached to the bottom of a vertical shaft suspended in the borehole.
- Melvyn Kay(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
Chapter 7Pumps
7.1 INTRODUCTION
Few water supply systems have the benefit of a gravity supply, most require some kind of pumping. Pumps are a means of adding energy to water. They convert fuel energy, such as petrol or diesel, into useful water energy using combustion engines or electric motors. In the typical pipe flow problem in Chapter 5 , the energy to drive water along the pipeline to the town was from a reservoir located high above the town. The energy line drawn from the reservoir to the town indicated the amount of energy available. Adding a pump to this system increases the available energy and raises the energy line so that the discharge from the reservoir to the town can be increased (Figure 7.1 ).Pumps have been used for thousands of years. Early examples were largely small hand or animal-powered pumps for lifting small quantities of water. It was not until the advent of the steam engine, only two centuries ago, that the larger rotating pumps were developed and became an important part of the study of hydraulics. Consequently, there are two main types of pump: positive displacement pumps , which are mostly small hand and animal-powered pumps still in common use in developing countries; and roto-dynamic pumps , those driven by diesel or electric motors and used in all modern water supply and irrigation systems.Because of the importance of pumping, most of this chapter is devoted to pumps, but mention is also made of turbines which are hydraulic machines for generating energy.7.2 POSITIVE DISPLACEMENT PUMPS
Positive displacement pumps usually deliver small discharges over a wide range of pumping heads. Typical examples are hand-piston pumps, rotary pumps, airlift pumps and Archimedean screws (Figure 7.2 ).Figure 7.1 Pumps add energy to pipe systems.7.2.1 Typical pumps
Hand-piston pumps (Figure 7.2a and e
eBook - ePubBiermann's Handbook of Pulp and Paper
Volume 2: Paper and Board Making
- Pratima Bajpai(Author)
- 2018(Publication Date)
- Elsevier(Publisher)
These rollers pinch the tubing and enclose small amounts of fluid and push them forward in the tubing. The pump acts as a check valve. Only the tubing is contacted by the material to be pumped so seals are not required. These pumps are usually fairly small and have flow rates on the order of less than 1 mL/min at low pressures, although large units using tubing of 65 mm inside diameter can pump 600 L/min at 220 psi. The pumps are useful for metering materials. Metering Pumps Positive displacement pumps are often used as metering pumps because they accurately control flow rates by changing the speed at which the pump is driven without regard to the back pressure. They are also used to pump relatively small volumes of liquids against high pressures. Possible metering pumps include leak-proof diaphragm pump, piston pump for precision, rotary designs for simplicity and low maintenance, or solenoid for proportional impulse control. The corrosive nature of the fluid to be pumped (which is usually a function of temperature) is a factor in the selection of a pump. A fluid that is listed as compatible with a pump material at room temperature may not be compatible at high temperatures. 23.4. Centrifugal (Dynamic) Pumps Introduction The impeller is the piece that rotates inside the casing to effect pumping (Fig. 23.5). The input of the pump is at the eye and the liquid enters perpendicular to the plane of the impeller in the volute or spiral design. As the impeller is never in contact with the case, the input and output are connected hydraulically. One important characteristic of centrifugal pumps is that they must be primed (filled with water) before they can generate suction to overcome any lift required for the liquid (i.e., if the source of water is below the pump)
- Barbara Renner(Author)
- 2017(Publication Date)
- Routledge(Publisher)
1.46 During operation, the fluid that is being pumped passes between the liner and the housing, much like an external gear pump. The pumping action, however, is similar to a peristaltic pump. As the eccentric rotates past the inlet port, it creates a negative pressure and allows fluid to be drawn into the vacant cavity between the liner and housing. At the same time, fluid that is trapped between the housing and liner ahead of the eccentric is forced out of the pump.1.47 Most of the pumps are powered by small fixed or variable speed A-C or D-C motors. Some manufacturers also provide pneumatic powered motors instead of the electrical varieties. Additionally, the motors can be manually adjusted to deliver the proper amount of chemical, or they can be connected electrically to an instrument monitoring device that senses the level of chemical in a fluid and adjusts the pump speed to match a preset level of chemical dosage.FLUID TRANSFER PUMPS1.48 Positive displacement style pumps that are used for fluid transfer are often only larger models of the chemical feed pumps that were previously described in this chapter. However, there are some additional types that are manufactured that were not described and have different construction features.1.49 Generally, positive displacement pumps are used to transfer fluids that have viscosities that are higher than water and do not flow easily. Therefore, they require pumps that have higher head capacities as well as the ability to handle these materials. Flow capacities over 300 gpm (gallons per minute) are common for many of the pumps, although, the general range is less than 100 gpm.1.50 The pump styles most frequently used include piston/plunger, rotary, diaphragm, progressive cavity, and peristaltic. Some styles can be used for a number of applications, while others are more commonly used to handle only a specific material.PLUNGER TRANSFER PUMPS1.51
eBook - ePub- Barbara Hauser(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
Chapter 14Positive Displacement Pumps
Whereas centrifugal pumps are meant for low pressure, high flow applications, positive displacement pumps can achieve greater pressures, but are slower moving, low flow pumps. They are used for pumping sludges and slurries and other high density or viscous fluids for which other types of pumps are inappropriate. Tolerances are close between stationary and moving parts, and flow is constant. A given volume of liquid is positively displaced with each pump cycle; there is no backwards slippage of fluid, and high shutoff pressures are developed. When pumping head increases from a blockage, or when system head increases, the pump will still move the same amount of fluid, but will draw more horsepower, and create high discharge pressure in overcoming that head.This is quite different from the operation of the centrifugal pump, which delivers less flow and uses less horsepower under high head conditions. With a positive displacement pump, total blockage of pump or line, whether caused by foreign material or a closed valve, will cause failure of pump, line or motor.Note: Never start a positive displacement pump with the discharge valve closed!These pumps operate at much slower speeds than centrifugal pumps. They are much larger, heavier, and more costly. The large number of moving parts (valves, cams, reciprocating components) make them more complex, and the close running clearances make them more subject to wear, with resulting parts replacements necessary. Efficiency is lower and maintenance cost higher than in the centrifugal pump.There are two basic categories of positive displacement pump: the reciprocating pumps, and the rotary pumps. Under reciprocating pumps are generally included the plunger, or piston pump, the diaphragm pump, and the peristaltic pump. Under rotary pumps are included the rotary gear pump, the vane pump, the progressive cavity pump, and the Archimedes screw.
