PumpsDOE-HDBK-1018/1-93POSITIVE DISPLACEMENT PUMPSPrincipleof OperationAll positive displacement pumps operate on the same basic principle. This principle can be mosteasily demonstrated by considering a reciprocating positive displacement pump consisting of asingle reciprocating piston in a cylinder with a single suction port and a single discharge port asshown in Figure 12. Check valves in the suction and discharge ports allow flow in only onedirection. During the suction stroke, the piston moves to the left, causing the check valve in the suctionFigure 12 Reciprocating Positive Displacement Pump Operationline between the reservoir and the pump cylinder to open and admit water from the reservoir.During the discharge stroke, the piston moves to the right, seating the check valve in the suctionline and opening the check valve in the discharge line. The volume of liquid moved by thepump in one cycle (one suction stroke and one discharge stroke) is equal to the change in theliquid volume of the cylinder as the piston moves from its farthest left position to its farthestright position.ReciprocatingPumpsReciprocating positive displacement pumps are generally categorized in four ways: direct-actingor indirect-acting; simplex or duplex; single-acting or double-acting; and power pumps.Rev. 0ME-03Page 19
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