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. Radial or Mixed Flow - In a radial flow pump, the liquid enters at the center of the impeller and is directed out along the impeller blades in a direction at right angles to the pump shaft. The pressure is developed wholly by centrifugal force. . Peripheral - Peripheral pumps employ a special impeller with a large number of radial blades. As the fluid is discharged from one blade, it is transferred to the root of the next blade and given additional energy. 10.1.2 Positive Displacement Pump Positive displacement pumps differ from centrifugal pump designs in that energy is added to the fluid periodically by the movement of control mechanisms causing displacement of fluid and an increase in pressure. A positive displacement pump unlike a centrifugal pump will produce the same flow at a given rotational or cyclic speed regardless of the discharge pressure. The positive displacement pump contains an expanding cavity on the suction side of the pump and a decreasing cavity on the discharge side. Fluid enters into the pump as the cavity on the suction side expands and the fluid is forced out of the discharge as the cavity collapses. Positive displacement pumps can be subdivided into reciprocating and rotary types and this principle applies to any individual reciprocating or rotary pump design. Positive displacement pumps deliver a definite volume of fluid for each cycle of pump operation. Therefore, the only factor that affects 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 affect the flow through the pump. As the discharge pressure of the pump increases, some amount of fluid leaks from the discharge of the pump back to the pump suction, thus reducing the effective flow rate of the pump. This fluid leakage from the pump discharge to the suction area is called slippage. Positive displacement pumps come in many designs and performance specifications, but they all work on the same principle. An increasing volume is opened to suction, filled, closed, moved to discharge, and displaced. The delivered capacity is nearly constant throughout the discharge pressure range. Reciprocating pump - A reciprocating pump is characterized by a back-and-forth motion of pistons inside of cylinders that provides the flow of fluid. Each stroke of a reciprocating pump delivers a definite volume of liquid to the system. The master cylinder of the automobile brake system is an example of a simple reciprocating pump. Reciprocating pumps include piston, plunger and diaphragm. Rotary pump - Rotary pumps operate on the principle that a rotating vane, screw, or gear traps the fluid on the suction side of the pump casing and forces it to the discharge side of the casing. A rotary displacement pump is different from a centrifugal pump in that in a centrifugal pump, the liquid displacement and pumping action depend on developed liquid velocity, while a rotary pump operates on the positive displacement Pumps 10-10 Revision C

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