Technology & Engineering
Pump Characteristics
Pump characteristics refer to the unique performance attributes of a pump, such as flow rate, head, efficiency, and power consumption. These characteristics determine the pump's suitability for specific applications and are crucial for selecting the right pump for a particular system. Understanding pump characteristics is essential for optimizing system performance and energy efficiency.
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6 Key excerpts on "Pump Characteristics"
eBook - PDFFlow of Industrial Fluids
Theory and Equations
- Raymond Mulley(Author)
- 2004(Publication Date)
- CRC Press(Publisher)
These pumps are highly specialized and are generally limited to heat transfer applications in the nuclear industry. We will discuss them briefly in Appendix AIII. C H A P T E R T H R E E 111-6: INHERENT AND INSTALLED CHARACTERISTICS OF PUMPS P u m p s - T h e o r y a n d E q u a t i o n s Pumps, like control valves, have inherent characteristics and installed characteristics. It is well to remember the distinction. We will give a rather detailed technical description in Appendix AIII. Inherent characteristics An inherent characteristic is one that is proper to the pump when all external influences have been eliminated. It is what the pump manufac- turer uses to describe his pump.This is done so a maximum of informa- tion can be transmitted in the most simplified form.The inherent charac- teristics are usually shown on the pump curve, and most of us are reason- ably familiar with that of the centrifugal pump.The basic curve is that of developed head in feet or meters of fluid versus the volumetric flow rate. It is up to the user to convert this basic data to a more useful form. If the reader gets into the habit of thinking of the developed head as energy per unit mass instead of feet or meters of fluid, he or she will avoid many potential pitfalls. The typical centrifugal pump curve gives the energy per unit mass that the pump transfers to the fluid plotted against the volumetric flow rate.The pump curve will give the appro- priate units in feet or meters and in gallons (U.S.) per minute or cubic meters per hour.
eBook - PDF- Paresh Girdhar, Octo Moniz(Authors)
- 2011(Publication Date)
- Newnes(Publisher)
Changes in design results in differences in Pump Characteristics and gives rise to a wide range of hydraulic properties; it often becomes difficult to compare one type of pump with another. To overcome this problem, non-dimensional characteristics are defined. In order to determine the dimensional characteristics of a geometrically similar pump based on a known dimensional characteristic of another pump, it is necessary to transform the known characteristic into a non-dimensional characteristic. To work out a non-dimensional characteristic, the normal operating point (the point at which the pump is supposed to operate at most of the times) is considered. The Flow rate, differential head, power, and efficiency are represented as Q n , H n , P n, and η n. These values are considered as 100% and the values deviating from the normal are expressed as percentages of the normal values. Once the Q n , H n , P n, and n η are known of the desired characteristics, it is easy to calculate the other values necessary for the drawing of the characteristic curves. The Power–flow rate curve shown under Section 5.1 is an example of the use of non-dimensional characteristics. There are basically two types of non-dimensional characteristics that are commonly used. These are: 1. Individual characteristics 2. Universal characteristics. 96 Practical Centrifugal Pumps The Individual characteristics are derived from the dimensional characteristics and these are that have been discussed above. The Universal characteristics are basically derived from the similarity of centrifugal pumps. These are the: • Head coefficient • Flow coefficient. Head Coefficient is represent by ψ and is obtained by the formula, 2 2 / 2 H u g ϕ = Flow Coefficient is represented by 2 Q u A φ = Where u 2 is the peripheral velocity at impeller outlet A = π /4 × d 2 2 – Area of impeller.
- Ron Palgrave(Author)
- 2003(Publication Date)
- Elsevier Science(Publisher)
Pi pe systern basics Synopsis Pumps arc normally selected to 'fit' the hydraulic characteristics of the system they operate in. Sometimes there are question marks and doubts about the precise nature of this characteristic, and we will deal with that later. However, to get a good 'fit' is the objective of every application engineer. To be given good 'fit' is the hope of every purchaser, since he infers this to mean the undoubted risks associated with mis-sclcction have been avoided. There are some simple rules describing pumping pipe system characteristics. Knowing how they relate to the pump characteristic can greatly reduce the risk of operation surprises. Background The point where the pump and system characteristics intersect dictates the 'fit'. However, there is more to a selection than just determining a 'fit'. We shall see later how the relationship between the pump characteristic curve and the system characteristic can influence the pumps behaviour. For example, it can determine how quicldy the pump appears to 'wear out'. The pump characteristic is experimentally determined by the manufacturer and is unique for each model in their range. Centrifugal Pump Characteristics share common features. The differences are often more important to the designer, than to the plant designer. The general features of Pump Characteristics have been covered earlier. The system characteristics, on the other hand, have a wide range of very different features. This can easily be demonstrated by describing 21 Troubleshooting Centrifugal Pumpsand their Systems characteristics for three stereotypical examples. The system curve is at least as important as the pump performance curve when attempting to solve pump scheme performance problems. As we shall see many times in the subsequent pages, the overall performance of any pumping scheme rests not just with the pump, but also with the pipe system behaviour.
eBook - ePubCavitation And The Centrifugal Pump
A Guide For Pump Users
- Edward Grist(Author)
- 2023(Publication Date)
- Routledge(Publisher)
Chapter 3 Centrifugal Pump Performance CharacteristicsPART 1. NON-CAVITATING PERFORMANCE
3.1 A Typical Characteristic
Non-cavitating centrifugal pump performance characteristics provide a base from which deviations caused by cavitation can be measured. The changes of interest are almost exclusively those which produce a drop in the generated head. A typical non-cavitating characteristic is shown in Fig. 3.1 .Most pumps run at a single speed. A pump characteristic for single speed operation, as shown by the solid lines in Fig. 3.1 , is normally available from the manufacturer. The essential parts of the characteristic can be, and often are, the subject of contractual acceptance tests.Fig. 3.1 Typical non-cavitating performance characteristics (ΔH/Q, PA /Q, η/Q)3.2 Affinity Relationships and Specific Speed
It is evident from Fig. 3.1 that a change in pump speed results in a significant change in the values of generated head and flowrate at, and near, best efficiency flowrate.Rules for calculating such changes are fundamental to the centrifugal pump selection process. These rules, commonly known as “affinity laws”, can be derived using a simplified form of dimensional analysis.Extending the analysis from a particular pump to a comparison of generic pump designs shows that both physical design factors and the shape of performance curves can be characterised by a single term, “specific speed”.The validity of relationships derived is limited to conditions where Q, ΔH, n and D are the only significant variables to describe pump performance. This holds true for most liquids. Pumps for liquids that fall outside this description are considered separately in section 3.4
eBook - PDF- Sulzer Pumps(Author)
- 2013(Publication Date)
- Elsevier Science(Publisher)
2.1 Typical characteristic curve shapes for centrifugal pumps. 40 Fig. 2.2 Typical pump characteristic with various impeller diameters and constant speed. 41 Ο 0,5 1 1.5 2 Fig. 2.3 Typical pump characteristic for constant impeller diameter and variable speed. 42 43 Fig. 2.4 Influence of specific speed on the shape of the characteristic. Fig. 2.5 shows a typical unstable characteristic, the system characteristic being intersected twice by the pump characteristic when for example the mains frequency drops. The pump may revert to minimum or zero delivery. The power input to the pump is then converted into heat. Pumps with unstable characteristics may resonate with the hydraulic system in closed circuits, leading to fluctuating flow rate. Stable characteristics are a fundamental necessity for the automatic control of centrifugal pumps. 200 180 140 0 20 40 60 80 100 120 140 160 Q in m 3 / h Fig. 2.5 Typical influence of an unstable characteristic on the operating behaviour of a pump under changes of frequency. 2.2 Control of centrifugal pumps 2.2.1 Piping system characteristic The head to be overcome consists of a geodetic component H g eo independent of the flow rate, and a head loss H d yn increasing with the square of the flow rate and depending only on pipework layout, pipe diameter and length. H g eo and H d yn are totalled and plotted against the flow rate (Fig. 2.6). The resulting curve is termed as the system head curve. Centrifugal pumps adjust themselves automatically to the intersection of the system and throttle characteristics. This intersection is the duty point. 44 While the geodetic head differs with variations in upstream and downstream levels, the dynamic head loss increases with the gradual incrustation of the pipework (Fig. 2.6). In borderline cases, the geodetic delivery head may be nil. System head curve 2.2.2 Control possibilities Pump output may be controlled by the following methods: 1.
eBook - PDFHeating, Ventilating, and Air Conditioning
Analysis and Design
- Faye C. McQuiston, Jerald D. Parker, Jeffrey D. Spitler(Authors)
- 2019(Publication Date)
- Wiley(Publisher)
Pump Characteristics for multiple pump applications are obtained in the same way as discussed earlier for series and parallel system elements. Figure 10-17 shows two identical pumps in parallel with their associated characteristics. Note the use of check valves to allow operation of a single pump. 10-4 PIPING SYSTEM FUNDAMENTALS There are many different types of piping systems used with HVAC components, and there are many specialty items and refinements that make up these systems. Chapters 12 and 13 of the ASHRAE Handbook, HVAC Systems and Equipment Volume (5) give a detailed description of various arrangements of the components making up the complete system. Chapter 33 of the ASHRAE Handbook, Fundamentals Volume (2) pertains to the sizing of pipe. The main thrust of the discussion to follow is to develop methods for the design of 314 Chapter 10 Flow, Pumps, and Piping Design Figure 10-17 Pump and system characteristics for parallel pumps. basic piping systems used to distribute hot and chilled water. The basic concepts will first be covered. The principles involved in designing larger variable-flow systems using secondary pumping will then be discussed in Section 10-5. Section 10-6 pertains to steam systems. Basic Open-Loop System A simple open-loop piping system is shown in Fig. 10-18. Characteristically an open-loop system will have at least two points of interface between the water and the atmosphere. The cooling tower of Fig. 10-18 shows the usual valves, filters, and fittings installed in this type of circuit. The isolation valves provide for maintenance without complete drainage of the system, whereas a ball or plug valve should be provided at the pump outlet for adjust- ment of the flow rate. Expansion joints and a rigid base support, to isolate the pump as previously discussed, are shown. Chapter 13 of the ASHRAE Handbook, HVAC Systems and Equipment Volume (5) illustrates various cooling tower arrangements.
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