Machinery's Handbook, 31st Edition
PUMPS 2801 Piston pumps and plunger pumps deliver pulsing flow. Axial piston pumps are designed with multiple pistons arranged axially to the motor. A tilted swashplate turns and actu- ates the pistons in sequence. More pistons in the pump produce smoother flow. Radial piston pumps have pistons arranged radially around a central cam that actuates them in sequence. Reciprocating piston and plunger pumps used for fluid transfer are typically either single acting or double acting, which means the piston delivers fluid on one or both directions of movement. These are driven with a crank arrangement or other reciprocat- ing mechanism. A simplex pump has one cylinder, and a duplex pump has two cylinders. Arrangements with more cylinders are possible. Gear pumps deliver pulsing flow at high pressures and fairly high flow capacities. They rely on close clearances to capture the fluid. This means that the fluid being moved must be free of particulate matter. These pumps perform best with viscous fluids. Lobe pumps de - liver pulsing flow. They are similar to gear pumps, but the lobes in mesh do not contact one another. These pumps are often used to move fluid with large particulate inclusions. The lobes are often non-metallic, and are suitable for handling delicate items in a fluid stream. Vane pumps deliver pulsing flow at moderately high pressures. They are comprised of a rotating set of vanes that capture and release fluid inside a round housing. Screw pumps deliver smooth flow at moderately high pressures. They are commonly found in single, double, and triple screw configurations. Single screw pumps are some times called progressing-cavity pumps. Direct acting pumps are driven by a fluid with a differential pressure, and generally use a piston. They can use air, steam, or a liquid as the driver. These pumps are suitable for high pressure, low flow applications. They have the disadvantage of consuming high volumes of drive fluid. Kinetic Pumps: Kinetic pumps generate momentum in a fluid, which is then transformed into pressure. These pumps do not have a fixed discharge volume, and therefore do not impart a pulsation to the fluid being moved. The most common type of kinetic pump is the centrifugal pump. Other types of kinetic pumps include air lifts, hydraulic rams, turbine pumps, and jet pumps Centrifugal pumps use a one or more spinning impellers to accelerate a fluid radially from the inlet. The fluid is then slowed by a spiral volute, converting the velocity energy into pressure energy. Centrifugal pumps can be radial, axial, and mixed flow types. The pump specific speed determines which would be the best type for a given application. Some centrifugal pumps are configured to handle fluids with solids. In those cases, a grinder can be integrated into the pump. Centrifugal pumps are used mainly in high flow applications with moderate heads. Multistage versions are suitable for high head applications. The size of a centrifugal pump is designated by the discharge port size, inlet port size, impeller diameter, and number of stages. Therefore, a 1 x 2 x 5 pump would be a single stage pump with a 1 inch discharge, a 2 inch inlet, and a 5 inch impeller. If the pump case is supported at the centerline of the shaft, it is said to be “centerline mounted”. This mounting configura - tion is ideal for high temperature applications because shaft alignment with the driver is maintained as the case expands due to heat. Foot mounted pumps are supported under the case, and frame mounted pumps are supported under the bearing housing. Air lift pumps use a stream of air bubbles injected into the submerged base of a pipe to entrain the fluid. The fluid rises with the air bubbles. These pumps are used when only light suction is needed. Hydraulic ram pumps operate cyclically to deliver pulsing flow. A hydraulic ram is typi cally comprised of a spring or weight loaded normally open valve, and a check valve. Flowing water with kinetic energy creates pressure against the normally open valve until it closes. This elevated pressure sends fluid through the check valve to a higher elevation. The check valve then prevents the fluid from reversing. Once pressure is relieved, the nor mally open valve opens once more and the cycle begins again. Turbine pumps are comprised of a series of progressive impellers. Each stage, or impel ler, increases the energy of the fluid. Jet pumps are commonly used in home water well
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