Dynamic Pumps

• Dynamic pumps continuously accelerate the fluid within the pump to a velocity much higher than the velocity at the discharge. The subsequent decrease of the fluid velocity at the discharge causes a corresponding increase in pressur the
• dynamic pump category is made up of centrifugal pumps and special effect pumps, such as eductor and hydraulic ram pumps. Eductors, or jet pumps as they are sometimes called, use a high-pressure stream of fluid to pump a larger volume of fluid at a lower pressure
• . An eductor consists of three basic parts: the nozzle, the suction chamber, and the diffuser. The highpressure fluid is directed through a nozzle to increase its velocity.
•  The high velocity creates a low-pressure area that causes the low-pressure fluid to be drawn into the suction chamber.
•  The low-pressure fluid is then mixed with the high velocity fluid as it flows through the diffuser, and the velocity energy of the mixture is converted into pressure at the discharge. Eductors commonly are used in powerplants and dams to dewater sumps below the inlet of the sump pumps
• . Some plants use eductors to pump cooling water for the units. By far, the most common type of dynamic pump is the centrifugal pump. The impeller of a centrifugal pump, the rotating component of the pump which imparts the necessary energy to the fluid to provide flow and pressure, is classified according to the direction of flow in reference to the axis of rotation of the impeller
• . The three major classes of centrifugal impellers are: 
• 1. Axial-flow 2. Radial-flow 3. Mixed-flow Impellers may be classified further by their construction.
•  The impeller construction may be:
•  1. Open 2. Semi-open 3. Closed
• An open impeller consists of vanes attached to a central hub. A semi-open impeller has a single shroud supporting the vanes, usually on the back of the impeller. The closed impeller incorporates shrouds on both sides of the vanes. 
• The shrouds totally enclose the impeller’s waterways and support the impeller vanes. Centrifugal pumps are also classified by the means in which the velocity energy imparted to the fluid by the impeller is converted to pressure. 
• Volute pumps use a spiral or volute shaped casing to change velocity energy to pressure energy. Pumps which use a set of stationary diffuser vanes to change velocity to pressure are called diffuser pumps. The most common diffuser type pumps are
•  vertical turbine pumps and single stage, low head, propeller pumps. Large volute pumps may also have diffuser vanes; but while these vanes direct the water flow, their main purpose is structural and not energy conversion.