Pump characteristic curves

Figure 3-50. Typical centrifugal pump characteristic curve vrith auxiliary specific speed curve. Double-suction, single-stage, 6-in. pump, operating at 1760 rpm constant speed. (By permission, Karassik, I. and Carter, B., Centrifugal Pumps, McGraw-Hill Book Co., inc., 1360, p. 197.)...

Most centrifugal pumps are controlled by throttling the flow with a valve on the pump discharge, see Section 5.8.3. This varies the dynamic pressure loss, and so the position of the operating point on the pump characteristic curve. 

Figure 8-2 Typical pump characteristic curves. (From TRW Mission Pump...

Most pump manufacturers provide composite curves, such as those shown in Fig. 8-3, that show the operating range of various pumps. For each pump that provides the required flow rate and head, the individual pump characteristics (such as those shown in Fig. 8-2 and Appendix H) are then consulted. The intersection of the system curve with the pump characteristic curve for a given impeller determines the pump operating point. The impeller diameter is selected that will produce the required head (or greater at the specified flow rate). This is repeated for all possible pump, impeller, and speed combinations to determine the combination that results in the highest efficiency (i.e., least power requirement). Note that if the operating point (Hp, Q) does not fall exactly on one of the (impeller) curves, then the... 

You must select a centrifugal pump that will develop a pressure of 40 psi when pumping a liquid with an SG of 0.88 at a rate of 300 gpm. From all the pump characteristic curves in Appendix H, select the best pump for this job. Specify pump head, impeller diameter, motor speed, efficiency, and motor horsepower. 

You must chose a centrifugal pump to pump a coal slurry. You have determined that the pump must deliver 200 gpm at a pressure of at least 35 psi. Given the pump characteristic curves in Appendix H, tell which pump you would specify (give pump size, speed, and impeller diameter) and why What is the efficiency of this pump at its operating point, what horsepower motor would be required to drive the pump, and what is the required NPSH of the pump The specific gravity of the slurry is 1.35. 

FIGURE 10 Typical centrifugal pump characteristic curves showing efficiency curves and NPSH (net positive suction head) for several impeller diameters. 

Pump Characteristic and System Head. The pump characteristic curve needs to be matched with the head loss through a piping system, which is known as the system head. The system head increases approximately in proportion to the square of the flow rate (Ap cc z/2). An example of a system head calculation is given in Section 3.10. 

Figure 22 Pump characteristics curves and system head. Adapted from Perry23...

Related Calculations. Use the similarity laws to extend or change the data obtained from centrifugal-pump characteristic curves. These laws are also useful in field calculations when the pump head, capacity, speed, or impeller diameter is changed. 

Related Calculations. Use this procedure for any centrifugal pump handling any liquid in any service—power, process, marine, industrial, or commercial. Pump manufacturers can supply a temperature-rise curve for a given model pump if it is requested. This curve is superimposed on the pump characteristic curve and shows the temperature rise accompanying a specific flow through the pump. 

Obtain the pump characteristic curves. Many manufacturers publish pump-down factor curves such as those in Fig. 6.36a and b. These curves are usually published as part of the engineering data for a given line of pumps. Obtain the curves from the manufacturers whose pumps are being considered. 

To select a centrifugal pump size we must examine pump characteristic curves, which are plots of head versus flow rate. Reference 8.21 discusses the factors... 

FIGURE 4.7 Setup for developing pump characteristics curves. 

FIGURE 4.8 Pump characteristic curves for a 375-mm impeller. (Courtesy of Smith and Loveless. With permission.)... 

Example 4.2 Pump characteristics curves are developed in accordance with the setup of Figure 4.7. The pressure at the outlet of the pump is found to be 196 kN/m gage. The discharge flow is 0.15 mVs and the outlet diameter of the discharge pipe is 375 mm. The motor driving the pump is 50 hp. Calculate TDH. 

Determine the operating point on the pump characteristic curve when the flow is such that the pressure drop across the control valve is 35 kN/m. ... 

For highly turbulent flow (i.e., constant Kfg), the required pump head is a quadratic function of the flow rate Q. This relation, which is superimposed on the pump characteristic curves (see line SI in Figure 5.9), is the operating line for the system. The actual pump head and the resulting flow rate are determined by the intersection of the operating line and the pump impeller characteristic curve. For the specified flow rate, the best (least cost) pump/impeller/motor combination that will provide this flow rate should be selected. 

Inequality constraints, g x, are expressions that involve any or all of the set of variables, i, and are used to bound the feasible region of operation. For example, when operating a centrifugal pump, the head developed decreases with increasing flow rate according to a pump characteristic curve. Hence, if the flow rate is varied when optimizing the process, care must be taken to make sure that the required pressure increase (head) does not exceed that available from the pump. The expression might be of the form. 

As far as modelling the decrease of flow rate with time after the loss of electric power is concerned, the codes used balance the momentum in each cooling circuit and in the core. This momentum balance is combined with the continuity equations, with the momentum balance of the pumps and with the pump characteristic curves. In these calculations the head losses are overestimated for sake of conservatism. 

For a given centrifugal pump operating at a constant speed, the flow rate through the pump is dependent upon the differential pressure or head developed by the pump. The lower the pump head, the higher the flow rate. A vendor manual for a specific pump usually contains a curve of pump flow rate versus pump head called a pump characteristic curve. After a pump is installed in a system, it is usually tested to ensure that the flow rate and head of the pump are within the required specifications. A typical centrifugal pump characteristic curve is shown in Figure 21.3. 

There are several terms associated with the pump characteristic curve that must be defined. Shutoff head is the maximum head that can be developed... 

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