Pumps performance, typical

System Curves In addition to the pump design, the operational performance of a pump depends upon factors such as the downstream load characteristics, pipe friction, and valve performance. Typically, head and flow follow the following relationship ... 

FIG. 10-31 Typical pump performance curve. The curve is shown for water at 85 F. If the specific gravity of the fluid is other than unity, BHP must he corrected. 

The pressure p used in Equation 3-32 is the differential developed pressure (across the pump inlet and outlet). Since the inlet suction pressure is usually small compared to the discharge pressure, the discharge pressure is used. Thus, this is the application resistance pressure in most cases. Figure. 3-54 shows a typical reciprocating pump performance. 

Figure 3-54. Typical power-pump performance (courtesy Ingersoll-Rand Co.).

For quick pump selection, manufacturers often give the most essential performance details for a whole range of pump sizes. Figure 10-40 shows typical performance data for a range of process pumps based on suction and discharge pipes and impeller diameters. The performance data consists of pump flow rate and head. Once a pump meets a required specification, then a more detailed performance data for the particular pump can be easily found based on the curve reference number. Figure 10-41 shows a more detailed pump performance curve that includes, in addition to pump head and flow, the brake horsepower required, NPSH required, number of vanes, and pump efficiency for a range of impeller diameters. 

Similar to the cooling rate and ultimate temperature tests for the condenser, evacuation rates and lowest achievable pressure are baseline tests that indicate the performance of the vacuum-pumping system. Typical evacuation rates permit reaching 10pm Hg within 20-30 min. The lowest achievable pressure is commonly 20pm Hg or less. 

Regional HAI can be accomplished using a hepatic arterial port, a totally implantable pump, or a percutaneously placed catheter into the hepatic artery that is connected to an external pump. The volume of drug required to administer floxuridine can be contained within an implantable pump, whereas fluorouracil administration generally requires use of an external pump. Implanted infusion pumps are typically loaded with a 2-week volume of chemotherapy that is followed by an infusion of heparinized saline for 2 weeks. Candidates are selected carefully based on documentation of hepatic-only disease, good performance status, and no significant comorbidities or liver anatomic variants. 

From the standpoint of predicting pump performance for different liquids, it is this lowered pressure within the cavitated region that is of primary importance. In order to evaluate these temperature and pressure effects, a fixed amount of cavitation was generated in nitrogen and water, after which the stabilized temperatures and pressures within the cavitated region were measured. Typical results are shown in Fig. 8. 

For onshore facilities, water may be supplied from local public water mains, storage tanks, lakes, and rivers. In these cases, a conventional horizontal pump is typically employed. The preferred design for onshore firewater pumps is a horizontal centrifugal type with a relatively flat performance curve (i.e., pressure versus volume).The discharge pressure is determined by the minimum residual pressure required at the most remote location of the facility, flowing its highest practical demand with allowances added for piping friction losses. 

Normal fire protection practices and standards recommend fire pumps be tested annually to determine performance levels. Common practice in the process industries is to trend the flow performance to prepare predictive maintenance and replacement forecasts. Such forecasts can predict poor pump performance and help maintenance organizations implement corrective actions before this occurs. Typically a variance of 5% or more from the rated pump curve warrants further investigation and improvement (NFPA 25, Chapter 8, and Appendix C). 

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