Centrifugal pumps total head

Total head, centrifugal pumps, 180, 183 Discharge, 205 Head curve, 198 Suction head, 184, 186 Suction lift, 184, 186 Type, 184 Tubing, 63, 64 Two-phase flow, 124 Calculations, 125-127 Flow patterns, chart, 124 System pressure drop, 125 Types of flow, 124, 125 Utilities check list, process design, 34 Vacuum,... 

Figure 3-60. Temperature rise in centrifugal pumps in terms of total head and pump efficiency. (By permission, Karassik, I. and Carter, R., Centrifugai Pumps, McGraw-Hill Book Co. Inc., 1960, p. 438.)...

Suction and discharge heads are determined the same as for centrifugal pumps. Total head and capacity are used in selecting the proper rotary pump from a manufacturer s data or curves. Since viscosity is quite important in the... 

It is important to recognize that a centrifugal pump will operate only along its performance curve [10, 11]. External conditions will adjust themselves, or must be adjusted in order to obtain stable operation. Each pump operates within a system, and the conditions can be anticipated if each component part is properly examined. The system consists of the friction losses of the suction and the discharge piping plus the total static head from suction to final discharge point. Figure 3-51 represents a typical system head curve superimposed on the characteristic curve for a 10 by 8-inch pump with a 12-inch diameter impeller. 

The static pressure difference will be independent of the fluid flow-rate. The dynamic loss will increase as the flow-rate is increased. It will be roughly proportional to the flow-rate squared, see equation 5.3. The system curve, or operating line, is a plot of the total pressure head versus the liquid flow-rate. The operating point of a centrifugal pump can be found by plotting the system curve on the pump s characteristic curve, see Example 5.3. 

The total head Ah developed by a centrifugal pump at a particular capacity Q is independent of the liquid density. Thus the higher the density of the liquid, the higher the pressure AP developed by the pump. The relationship between AP and Ah is given by equation 4.10... 

Thus if a centrifugal pump develops a total head of 100 m when pumping a liquid of density p = 1000 kg/m3, the pressure developed is 981000 Pa while for p = 917 kg/m3 the pressure developed is 900000 Pa. 

Total head against capacity characteristic curve fora volute centrifugal pump... 

A centrifugal pump will operate normally at a point on its total head against capacity characteristic curve until the available NPSH falls below the required NPSH curve. Beyond this point, the total head generated by a centrifugal pump falls drastically as shown in Figure 4.6 as the pump begins to operate in cavitation conditions. 

System total heads should be estimated as accurately as possible. Safety factors should never be added to these estimated total head values. This is illustrated by Figure 4.8. Suppose that OAi is the correct curve and that the centrifugal pump is required to operate at point A. Let a safety factor be added to the total head values to give a system curve OA2. On the basis of curve OA2, the manufacturer will supply a pump to operate at point A2. However, since the true system curve is OA, the pump will operate at point Ai. Not only is the capacity higher than that specified, but the pump motor may be overloaded. 

Consider a centrifugal pump with an impeller diameter D operating at a rotational speed N2 and developing a total head Ahx. Consider an homologous pump with an impeller diameter D2 operating at a rotational speed N2 and developing a total head Ah2. 

Consider two centrifugal pumps in series as shown in Figure 4.10. The total head for the pump combination AhT is the sum of the total heads for the two pumps, ie... 

The piping and valves may be arranged to enable two centrifugal pumps to be operated either in series or in parallel. For two identical pumps, series operation gives a total head of 2Ah at a capacity Q and parallel operation gives a capacity of 2Q at a total head Ah. The efficiency of either the series or parallel combination is practically the same as for a single pump. 

A centrifugal pump is used to pump a liquid in steady turbulent flow through a smooth pipe from one tank to another. Develop an expression for the system total head A/t in terms of the static heads on the discharge and suction sides zd and zs respectively, the gas pressures above the tanks on the discharge and suction sides Pd and Ps respectively, the liquid density p, the liquid dynamic viscosity p, the gravitational acceleration g, the total equivalent lengths on... 

A centrifugal pump operates in this particular system with a total head against mean velocity curve represented by the equation... 

Two centrifugal pumps are connected in series in a given pumping system. Plot total head Ah against capacity Q pump and system curves and determine the operating points for... 

The higher flow rate might also reduce the head that the centrifugal pump produces if we are out on the pump curve where head is dropping rapidly with throughput. For simplicity, let us assume that the pump curve is flat. This means that the total pressure drop across the heat exchanger and the control valve is constant. Therefore, the pressure drop over the control valve must decrease as the the pressure drop over the heat exchanger increases. 

What is the upper limit of specific speed and capacity of a 1750-r/min single-stage double-suction centrifugal pump having a shaft that passes through the impeller eye if it handles clear water at 85°F (302 K) at sea level at a total head of 280 ft with a 10-ft suction lift What is the efficiency of the pump and its approximate impeller shape ... 

As a general guide, single-suction centrifugal pumps handle up to 50 gal/min (0.0032 m3/s) at total heads up to 50 ft (15 m) either single- or double-suction pumps are used for the flow rates to 1000 gal/min (0.063 m3/s) and total heads to 300 ft (91 m) beyond these capacities and heads, double-suction or multistage pumps are generally used. 

Chapter 5 considered pump types and their evaluation and selection. After selecting a pump type, the next step is to size the pump. This requires calculating the flow rate and the pressure rise across the pump or the pump head. The net positive suction head (NPSH), is also important, particularly for centrifugal pumps. NPSH is the difference between the total pressure and the vapor pressure of the fluid at the pump inlet. NPSH will be discussed later. 

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