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Mechanical Science HandbooksMechanical Science Handbooks 10000 Part 13

Tham khảo tài liệu 'mechanical science handbooksmechanical science handbooks 10000 part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Pumps DOE-HDBK-1018 1-93 POSITIVE DISPLACEMENT PUMPS Figure 20 Diaphragm Pump Positive Displacement Pump Characteristic Curves Positive displacement pumps deliver a definite volume of liquid for each cycle of pump operation. Therefore the only factor that effects flow rate in an ideal positive displacement pump is the speed at which it operates. The flow resistance of the system in which the pump is operating will not effect the flow rate through the pump. Figure 21 shows the characteristic curve for a positive displacement pump. The dashed line in Figure 21 shows actual positive displacement pump performance. This line reflects the fact that as the discharge pressure of the pump increases some amount of liquid will leak from the discharge of the pump back to the pump suction reducing the effective flow rate of the pump. The rate at which liquid leaks from the pump discharge to its suction is called slippage. Figure 21 Positive Displacement Pump Characteristic Curve Rev. 0 Page 27 ME-03 POSITIVE DISPLACEMENT PUMPS DOE-HDBK-1018 1-93 Pumps Positive Displacement Pump Protection Positive displacement pumps are normally fitted with relief valves on the upstream side of their discharge valves to protect the pump and its discharge piping from overpressurization. Positive displacement pumps will discharge at the pressure required by the system they are supplying. The relief valve prevents system and pump damage if the pump discharge valve is shut during pump operation or if any other occurrence such as a clogged strainer blocks system flow. Summary The important information in this chapter is summarized below. Positive Displacement Pumps Summary The flow delivered by a centrifugal pump during one revolution of the impeller depends upon the head against which the pump is operating. The positive displacement pump delivers a definite volume of fluid for each cycle of pump operation regardless of the head against which the pump is operating. Positive displacement pumps may be