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A pump is a device used for the transportation of gases, liquids, and slurries. Its general functionality is basic: a suction mechanism draws material in and a counter pressure is developed to force the material out at the other end.

It is used in a wide variety of applications including drainage, sewage, and irrigation. It also helps manage the transportation of highly volatile materials for the chemical and petroleum industries as well as the medical field.

Contents

[edit] Types

There are many different kids of pumps, but they can be categorized into two main types: dynamic and positive-displacement.

[edit] Dynamic

Dynamic pumps operate by developing high liquid velocity and converting that velocity into pressure in a diffusing flow passage.[1] Generally, dynamic pumps have a lower efficiency rate than positive displacement pumps, but they also have lower maintenance requirements.[2] They are capable of operating at high speeds and high fluid flow rates. Dynamic pumps exist in two different types of models: axial and centrifugal pumps.

[edit] Axial

Also called a propeller pump. They develop pressure through the propelling or lifting action of vanes on the liquid.[3] When dealing with high pressure, these pumps can operate with siphonic action until back pressure places the hydraulic gradient above the pump.[4] These pumps are often used in wet-pit drainage, low-pressure irrigation, and storm-water applications.

[edit] Centrifugal

A basic centrifugal pump design consists of an impeller and intake at its center. When the impeller rotates, the liquid is discharged by centrifugal force into a casing surrounding the impeller. The casing gradually decreases the velocity of the fluid, while the impeller continues at high velocity. This velocity is converted to pressure, which is necessary to discharge the fluid.[5] Centrifugal pumps offer smooth flow throughout the pump; uniform pressure in the discharge pipe, and their operating speed allows for direct connection to steam turbines and electric motors. Centrifugal pumps account for approximately 80 percent of the world’s pump production because “it is more suitable for handling large capacities of liquids than the positive displacement pump.”[6]

[edit] Positive-displacement

Positive-displacement pumps operate by forcing a fixed volume of fluid from the inlet pressure section of the pump into the discharge zone. Generally, these pumps are larger than equal capacity dynamic pumps. They offer fixed displacement per revolution and, within mechanical limitation, infinite pressure to move fluids.[7] They provide constant flow regardless of system pressure; however, the flow will increase as viscosity increases. Positive displacement pumps exist in three main types: reciprocating, metering, and rotary.

[edit] Reciprocating

Liquid is drawn into a cylinder through a suction valve on the intake stroke and discharged under positive pressure through the outlet valves on the discharge stroke. This pump releases a pulsating discharge that only changes with the speed of the pump. To provide smoother flow of fluid, an air chamber is often connected to the discharge side of the pump. This type of pump is generally used for sludge or slurry materials.

[edit] Metering

Also called a proportioning or controlled-volume pump. These pumps are available in a diaphragm or packed plunger style. They provide precision control of very low flow rates and are designed for clean service. So, dirty liquids easily clog their valve and nozzle connections.

[edit] Rotary

Traps fluid in its closed casing and discharges it with a smooth flow. It has a simple design that is “efficient” in handling flow conditions that are usually too low for centrifugal pumps.[8] It can handle nearly any liquid that does not contain abrasive solids, including viscous liquids. However, when it pumps highly viscous fluids, it must be operating at a reduced speed otherwise the flow rate will be too fast to fill the casing.

[edit] References

  1. Dynamic Pump. RPI. 2008-09-30.
  2. Dynamic Pump. RPI. 2008-09-30.
  3. Dynamic Pump. RPI. 2008-09-30.
  4. Dynamic Pump. RPI. 2008-09-30.
  5. Dynamic Pump. RPI. 2008-09-30.
  6. Dynamic Pump. RPI. 2008-09-30.
  7. Dynamic Pump. RPI. 2008-09-30.
  8. Positive Pump. RPI. 2008-09-30.