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Pump
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A pump is a device used to move fluids, such as gases, liquids or slurries. A pump displaces a volume by physical or mechanical action. One common misconception about pumps is the thought that they create pressure. Pumps alone do not create pressure they only displace fluid causing a flow.
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A pump is a device used to move fluids, such as gases, liquids or slurries. A pump displaces a volume by physical or mechanical action. One common misconception about pumps is the thought that they create pressure. Pumps alone do not create pressure they only displace fluid causing a flow. Adding resistance to flow causes pressure.
The earliest type of pump was the Archimedes screw, first used by Sennacherib, King of Assyria, for the water systems at the Hanging Gardens of Babylon and Nineveh in the 7th century BC, and later described in more detail by Archimedes in the 3rd century BC. In the 13th century AD, al-Jazari described and illustrated different types of pumps, including a reciprocating pump, double-action pump, suction pump, and piston pump.
In Indian mythology, Lord Krishna playfully splashed colors on Gopees using a "Pichkaaree", which was, and is even now, a reciprocating hand pump. Hence historically "Pichkaaree" should be recognized as the first pump, ever devised.
Types
Pumps fall into two major groups: positive displacement pumps and rotodynamic pumps . Their names describe the method for moving a fluid.
Positive displacement pumps
A positive displacement pump causes a fluid to move by trapping a fixed amount of it then forcing (displacing) that trapped volume into the discharge pipe. A positive displacement pump can be further classified as either
- a rotary-type, for example, the lobe, external gear, internal gear, screw, shuttle block, flexible vane or sliding vane pumps,
- the Wendelkolben pump or the helical twisted Roots pump.
- the liquid ring vacuum pump
Roots-type pumps
The low pulsation rate and gentle performance of this Roots-type positive displacement pump is achieved due to a combination of its two 90° helical twisted rotors, and a triangular shaped sealing line configuration, both at the point of suction and at the point of discharge. This design produces a continuous and non-vorticuless flow with equal volume. High capacity industrial "air compressors" have been designed to employ this principle as well as most "superchargers" used on internal combustion engines.
Reciprocating-type pumps
Reciprocating-type pumps use a piston and cylinder arrangement with suction and discharge valves integrated into the pump. Pumps in this category range from having "simplex" one cylinder, to in some cases "quad" four cylinders or more. Most reciprocating-type pumps are "duplex" (two) or "triplex" (three) cylinder. Furthermore, they are either "single acting" independent suction and discharge strokes or "double acting" suction and discharge in both directions. The pumps can be powered by air, steam or through a belt drive from an engine or motor. This type of pump was used extensively in the early days of steam propulsion (19th century) as boiler feed water pumps. Though still used today, reciprocating pumps are typically used for pumping highly viscous fluids including concrete and heavy oils.
Compressed-air-powered double-diaphragm pumps
Another modern application of positive displacement pumps are compressed-air-powered double-diaphragm pumps. Run on compressed air these pumps are intrinsically safe by design, although all manufacturers offer ATEX certified models to comply with industry regulation. Commonly seen in all areas of industry from shipping to process, SandPiper, Wilden Pumps or ARO are generally the larger of the brands. They are relatively inexpensive and can be used for almost any duty from pumping water out of bunds, to pumping hydrochloric acid from secure storage (dependant on how the pump is manufactured - elastomers / body construction). Suction is normally limited to roughly 6m although heads can be almost unlimited.
Kinetic pumps
- Continuous energy
- Conversion of added energy to increase in kinetic energy (increase in velocity)
- Conversion of increased velocity to increase in pressure
- Conversion of kinetic head to pressure head
- Meet all heads like kinetic, potential, and pressure
Application
Pumps are used throughout society for a variety of purposes. Early applications includes the use of the windmill or watermill to pump water. Today, the pump is used for irrigation, water supply, gasoline supply, air conditioning systems, refrigeration (usually called a compressor), chemical movement, sewage movement, flood control, marine services, etc.
Because of the wide variety of applications, pumps have a plethora of shapes and sizes: from very large to very small, from handling gas to handling liquid, from high pressure to low pressure, and from high volume to low volume.
Liquid and slurry pumps can lose prime and this will require you to prime the pump by adding liquid to the pump and inlet pipes to get the pump started. Loss of "prime" is usually due to ingestion of air into the pump. The clearances and displacement ratios in pumps used for liquids and other more viscus fluids cannot displace the air due to its lower density.
Specifications
Pumps are commonly rated by horsepower, flow rate, outlet pressure in feet of head, inlet suction in suction feet of head.
Feet is the number of feet the pump can raise or lower a column of water at atmospheric pressure.
Pumps as public water supplies
One sort of pump once common worldwide was a hand-powered water pump over a water well where people could work it to extract water, before most houses had individual water supplies.
From this came the expression "parish pump" for "the sort of matter chattered about by people when they meet when they go to get water", "matter of only local interest". However water from pitcher pumps are more prone to contamination since it is drawn directly from the soil and does not undergo filtration, this might cause gastrointestinal related diseases.
Today, hand operated village pumps are considered the most sustainable low cost option for safe water supply in resource poor settings, often in rural areas in developing countries. A hand pump opens access to deeper groundwater that is often not polluted and also improves the safety of a well by protecting the water source from contaminated buckets. Pumps like the are designed to be cheap to build and install, and easy to maintain with simple parts. However, scarcity of spare parts for these type of pumps in some regions of Africa has diminished their utility for these areas.
Pump Efficiency
Pump efficiency is an important aspect and pumps should be be regularly tested. Thermodynamic pump testing is one method.
Pumping Energy
Energy needed to pump a given flow against a given head and pipe size, can be calculated using this spread sheet
Various aspects of pumping energy usage are covered in Energy is consumed by the pump, and also lost in the pipework and these must be considered.
See also
Gallery
Further reading
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- - Pump and pump system information
- Australian Pump Technical Handbook, 3rd edition, 1987, Australian Pump Manufacturers' Association Ltd
- Publications of and
- - Pump education devoted primarily to rotary positive displacement pumps
- Feb 1919 Popular Science article about how a homeowner can easily build a pressurized home water system that does not use electricity: Homemade Water Pressure Systems, Popular Science monthly, February 1919, page 83-84, Scanned by Google Books: http://books.google.com/books?id=7igDAAAAMBAJ&pg=PA83
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