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A small, electrically powered pump
A large, electrically driven pump (electropump) for waterworks near the Hengsteysee, Germany.

A pump is a device used to move fluids, such as liquids or slurries, or gases. 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. Pumps fall into five major groups: direct lift, displacement, velocity, buoyancy and gravity pumps.[1] Their names describe the method for moving a fluid.

Contents

Types

Displacement pumps

Mechanism of a scroll pump

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 according to the mechanism used to move the fluid:

Positive displacement rotary pumps are pumps that move fluid using the principles of rotation. The vacuum created by the rotation of the pump captures and draws in the liquid. Rotary pumps are very efficient because they naturally remove air from the lines, eliminating the need to bleed the air from the lines manually. Positive displacement rotary pumps also have their weaknesses. Because of the nature of the pump, the clearance between the rotating pump and the outer edge must be very close, requiring that the pumps rotate at a slow, steady speed. If rotary pumps are operated at high speeds, the fluids will cause erosion, much as ocean waves polish stones or erode rock into sand. Rotary pumps that experience such erosion eventually show signs of enlarged clearances, which allow liquid to slip through and detract from the efficiency of the pump. Positive displacement rotary pumps can be grouped into three main types. Gear pumps are the simplest type of rotary pumps, consisting of two gears laid out side-by-side with their teeth enmeshed. The gears turn away from each other, creating a current that traps fluid between the teeth on the gears and the outer casing, eventually releasing the fluid on the discharge side of the pump as the teeth mesh and go around again. Many small teeth maintain a constant flow of fluid, while fewer, larger teeth create a tendency for the pump to discharge fluids in short, pulsing gushes. Screw pumps are a more complicated type of rotary pumps, featuring two screws with opposing thread —- that is, one screw turns clockwise, and the other counterclockwise. The screws are each mounted on shafts that run parallel to each other; the shafts also have gears on them that mesh with each other in order to turn the shafts together and keep everything in place. The turning of the screws, and consequently the shafts to which they are mounted, draws the fluid through the pump. As with other forms of rotary pumps, the clearance between moving parts and the pump's casing is minimal. Moving vane pumps are the third type of rotary pumps, consisting of a cylindrical rotor encased in a similarly shaped housing. As the rotor turns, the vanes trap fluid between the rotor and the casing, drawing the fluid through the pump.

Positive Displacement Pumps has an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pumps as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. The volume is constant given each cycle of operation.

The positive displacement pumps can be divided into two main classes

  • reciprocating
  • rotary

The positive displacement principle applies whether the pump is a

  • rotary lobe pump
  • progressing cavity pump
  • rotary gear pump
  • piston pump
  • diaphragm pump
  • screw pump
  • gear pump
  • Hydraulic pump
  • vane pump
  • regenerative (peripheral) pump
  • peristaltic

Positive Displacement Pumps, unlike Centrifugal or Roto-dynamic Pumps, will produce the same flow at a given speed (RPM) no matter the discharge pressure.

  • Positive Displacement Pumps are "constant flow machines"

A Positive Displacement Pump must not be operated against a closed valve on the discharge side of the pump because it has no shut-off head like Centrifugal Pumps. A Positive Displacement Pump operating against a closed discharge valve, will continue to produce flow until the pressure in the discharge line are increased until the line bursts or the pump is severely damaged - or both.

A relief or safety valve on the discharge side of the Positive Displacement Pump is therefore absolutely necessary. The relief valve can be internal or external. The pump manufacturer normally has the option to supply internal relief or safety valves. The internal valve should in general only be used as a safety precaution, an external relief valve installed in the discharge line with a return line back to the suction line or supply tank is recommended.

Reciprocating Pumps

Typical reciprocating pumps are

  • plunger pumps
  • diaphragm pumps

A plunger pump consists of a cylinder with a reciprocating plunger in it. The suction and discharge valves are mounted in the head of the cylinder. In the suction stroke the plunger retracts and the suction valves open causing suction of fluid into the cylinder. In the forward stroke the plunger pushes the liquid out of the discharge valve.

With only one cylinder the fluid flow varies between maximum flow when the plunger moves through the middle positions, and zero flow when the plunger is at the end positions. A lot of energy is wasted when the fluid is accelerated in the piping system. Vibration and "water hammer" may be a serious problem. In general the problems are compensated for by using two or more cylinders not working in phase with each other.

In diaphragm pumps, the plunger pressurizes hydraulic oil which is used to flex a diaphragm in the pumping cylinder. Diaphragm valves are used to pump hazardous and toxic fluids.

Gear pump

This uses two meshed gears rotating in a closely fitted casing. Fluid is pumped around the outer periphery by being trapped in the tooth spaces. It does not travel back on the meshed part, since the teeth mesh closely in the centre. Widely used on car engine oil pumps.

Progressing cavity pump

Widely used for pumping difficult materials such as sewage sludge contaminated with large particles, this pump consists of a helical shaped rotor, about 10 times as long as its width. This can be visualized as a central core of diameter x, with typically a curved spiral wound around of thickness half x, although of course in reality it is made from one casting. This shaft fits inside a heavy duty rubber sleeve, of wall thickness typically x also. As the shaft rotates, fluid is gradually forced up the rubber sleeve. Such pumps can develop very high pressure at quite low volumes.

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, and even a brand of civil defense siren, the Federal Signal Corporation's Thunderbolt.

Peristaltic pump

Rotary peristaltic pump

A peristaltic pump is a type of positive displacement pump used for pumping a variety of fluids. The fluid is contained within a flexible tube fitted inside a circular pump casing (though linear peristaltic pumps have been made). A rotor with a number of "rollers", "shoes" or "wipers" attached to the external circumference compresses the flexible tube. As the rotor turns, the part of the tube under compression closes (or "occludes") thus forcing the fluid to be pumped to move through the tube. Additionally, as the tube opens to its natural state after the passing of the cam ("restitution") fluid flow is induced to the pump. This process is called peristalsis and is used in many biological systems such as the gastrointestinal tract.

Reciprocating-type pumps

Hand-operated, reciprocating, positive displacement, water pump in Košice-Ťahanovce, Slovakia (walking beam pump).

Reciprocating pumps are those which cause the fluid to move using one or more oscillating pistons, plungers or membranes (diaphragms).

Reciprocating-type pumps require a system of suction and discharge valves to ensure that the fluid moves in a positive direction. 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 can be 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 and special applications demanding low flow rates against high resistance.

Buoyancy pump

Compressed-air-powered double-diaphragm pumps

One modern application of positive displacement diaphragm pumps is 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 processing, 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 (dependent on how the pump is manufactured - elastomers / body construction). Lift is normally limited to roughly 6m although heads can reach almost 200 Psi.[citation needed]

Impulse pumps

Hydraulic ram pumps

A hydraulic ram is a water pump powered by hydropower.

It functions as a hydraulic transformer that takes in water at one "hydraulic head" (pressure) and flow-rate, and outputs water at a higher hydraulic-head and lower flow-rate. The device utilizes the water hammer effect to develop pressure that allows a portion of the input water that powers the pump to be lifted to a point higher than where the water originally started.

The hydraulic ram is sometimes used in remote areas, where there is both a source of low-head hydropower, and a need for pumping water to a destination higher in elevation than the source. In this situation, the ram is often useful, since it requires no outside source of power other than the kinetic energy of flowing water.

Velocity pumps

A centrifugal pump uses a spinning "impeller" which has backward swept arms

Rotodynamic pumps (or dynamic pumps) are a type of velocity pump in which kinetic energy is added to the fluid by increasing the flow velocity. This increase in energy is converted to a gain in potential energy (pressure) when the velocity is reduced prior to or as the flow exits the pump into the discharge pipe. This conversion of kinetic energy to pressure can be explained by the First law of thermodynamics or more specifically by Bernoulli's principle. Dynamic pumps can be further subdivided according to the means in which the velocity gain is achieved.

These types of pumps have a number of characteristics:

  1. Continuous energy
  2. Conversion of added energy to increase in kinetic energy (increase in velocity)
  3. Conversion of increased velocity (kinetic energy) to an increase in pressure head

One practical difference between dynamic and positive displacement pumps is their ability to operate under closed valve conditions. Positive displacement pumps physically displace the fluid; hence closing a valve downstream of a positive displacement pump will result in a continual build up in pressure resulting in mechanical failure of either pipeline or pump. Dynamic pumps differ in that they can be safely operated under closed valve conditions (for short periods of time).

Centrifugal pump

A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure and flow rate of a fluid. Centrifugal pumps are the most common type of pump used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward or axially into a diffuser or volute chamber, from where it exits into the downstream piping system. Centrifugal pumps are typically used for large discharge through smaller heads.

The screw centrifugal impeller was invented in 1960 by the late Martin Stähle, the founder of Hidrostal AG. He had received an order from the Amial S.A. fish processing factory in Chimbote (Peru) for the development of a system for transporting fish from the nets into a boat, and from the boat into the fish processing plant. The pump was to work reliably without damaging the fish. The result was the pump with the characteristic screw centrifugal impeller. This invention was a great success. It has since been used in many ways throughout the world in countless other fluid handling systems.

The screw centrifugal pump is a popular choice for handling delicate products such as food and crystals. Its low shear characteristic reduces emulsification when pumping mixtures making it ideal for pumping oily water and Return Activated Sludge [RAS] as it does not damage the floc. The pump's ability to pass long fibrous materials such as rope without clogging makes it a frequent choice for municipal waste water applications. A screw centrifugal pump typically has an operating efficiency of 70% to 85%. It has a relatively steeply rising head/capacity curve shape giving it good flow control capability over its allowable operating range

The impeller has a single blade, axially extended at the inlet and developed around its axis much like a corkscrew. Linking this to a centrifugal outlet allows pumping with the minimum of agitation and shear, essential factors when product bruising, liquid emulsification or clogging is to be avoided.

The screw centrifugal impeller features:

  • Large free passages for pumping liquid with solid objects and fibrous materials
  • Able to pump liquids and viscosity's above values normally possible with conventional centrifugal pumps
  • Steep H/Q curves with closed valve twice best efficiency point
  • Low NPSH characteristics
  • Flat non-overloading power curves
  • High hydraulic efficiencies

Screw centrifugal impeller pumps are widely accepted as state of the art pumps for handling raw sewage and sludges on treatment plants and incorporate many features, which benefits the end user. Screw centrifugal impeller pumps are ideal for handling raw sewage, which contains stringy fibrous material and for handling sewage sludge with up to 10% dry solids content. Typical application areas:

  • Sump emptying
  • Industrial effluent treatment
  • Feeding oily water separators
  • Transfer of 'live' fish
  • Oil and Chemical spillages
  • Mine Drainage
  • Processing of waste oils & sludges
  • Transfer of fruit and vegetables
  • Municipal waste water treatment plants

Centrifugal pumps are most often associated with the radial flow type. However, the term "centrifugal pump" can be used to describe all impeller type rotodynamic pumps[2] including the radial, axial and mixed flow variations.

Radial flow pumps

Often simply referred to as centrifugal pumps. The fluid enters along the axial plane, is accelerated by the impeller and exits at right angles to the shaft (radially). Radial flow pumps operate at higher pressures and lower flow rates than axial and mixed flow pumps.

Axial flow pumps

Axial flow pumps differ from radial flow in that the fluid enters and exits along the same direction parallel to the rotating shaft. The fluid is not accelerated but instead "lifted" by the action of the impeller. They may be likened to a propeller spinning in a length of tube. Axial flow pumps operate at much lower pressures and higher flow rates than radial flow pumps.

Mixed flow pumps

Mixed flow pumps, as the name suggests, function as a compromise between radial and axial flow pumps, the fluid experiences both radial acceleration and lift and exits the impeller somewhere between 0-90 degrees from the axial direction. As a consequence mixed flow pumps operate at higher pressures than axial flow pumps while delivering higher discharges than radial flow pumps. The exit angle of the flow dictates the pressure head-discharge characteristic in relation to radial and mixed flow.

Eductor-jet pump

This uses a jet, often of steam, to create a low pressure. This low pressure sucks in fluid and propels it into a higher pressure region.

Gravity pumps

Gravity pumps include the syphon and qanat or foggara.

Pump Repairs

Examining pump repair records and MTBF (mean time between failures) is of great importance to responsible and conscientious pump users. In view of that fact, the preface to the 2006 Pump User’s Handbook alludes to "pump failure" statistics. For the sake of convenience, these failure statistics often are translated into MTBF (in this case, installed life before failure).[3]

In early 2005, Gordon Buck, John Crane Inc.’s chief engineer for Field Operations in Baton Rouge, LA, examined the repair records for a number of refinery and chemical plants to obtain meaningful reliability data for centrifugal pumps. A total of 15 operating plants having nearly 15,000 pumps were included in the survey. The smallest of these plants had about 100 pumps; several plants had over 2000. All facilities were located in the United States. In addition, all plants had some type of pump reliability program in progress. Some of these programs could be considered as "new," others as "renewed" and still others as "established." Many of these plants—but not all—had an alliance arrangement with John Crane. In some cases, the alliance contract included having a John Crane Inc. technician or engineer on-site to coordinate various aspects of the program.

Not all plants are refineries, however, and different results can be expected elsewhere. In chemical plants, pumps have traditionally been "throw-away" items as chemical attack can result in limited life. Things have improved in recent years, but the somewhat restricted space available in "old" DIN and ASME-standardized stuffing boxes places limits on the type of seal that can be fitted. Unless the pump user upgrades the seal chamber, only the more compact and simple versions can be accommodated. Without this upgrading, lifetimes in chemical installations are generally believed to be around 50 to 60 percent of the refinery values.

It goes without saying that unscheduled maintenance often is one of the most significant costs of ownership, and failures of mechanical seals and bearings are among the major causes. Keep in mind the potential value of selecting pumps that cost more initially, but last much longer between repairs. The MTBF of a better pump may be one to four years longer than that of its non-upgraded counterpart. Consider that published average values of avoided pump failures range from $2600 to $12,000. This does not include lost opportunity costs. One pump fire occurs per 1000 failures. Having fewer pump failures means having fewer destructive pump fires.

As has been noted, a typical pump failure based on actual year 2002 reports, costs $5,000 on average. This includes costs for material, parts, labor and overhead. Let us now assume that the MTBF for a particular pump is 12 months and that it could be extended to 18 months. This would result in a cost avoidance of $2,500/yr—which is greater than the premium one would pay for the reliability-upgraded centrifugal pump.[3][4][5]

Applications

Metering pump for gasoline and additives.

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 the pump to be primed 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.

Pumps as public water supplies

First European depiction of a piston pump, by Taccola, c.1450.[6]

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 Afridev pump 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.[citation needed]

Sealing Multiphase Pumping Applications

Multiphase pumping applications, also referred to as tri-phase, have grown due to increased oil drilling activity. In addition, the economics of multiphase production is attractive to upstream operations as it leads to simpler, smaller in-field installations, reduced equipment costs and improved production rates. In essence, the multiphase pump can accommodate all fluid stream properties with one piece of equipment, which has a smaller footprint. Often, two smaller multiphase pumps are installed in series rather than having just one massive pump.

For midstream and upstream operations, multiphase pumps can be located onshore or offshore and can be connected to single or multiple wellheads. Basically, multiphase pumps are used to transport the untreated flow stream produced from oil wells to downstream processes or gathering facilities. This means that the pump may handle a flow stream (well stream) from 100 percent gas to 100 percent liquid and every imaginable combination in between. The flow stream can also contain abrasives such as sand and dirt. Multiphase pumps are designed to operate under changing/fluctuating process conditions. Multiphase pumping also helps eliminate emissions of greenhouse gases as operators strive to minimize the flaring of gas and the venting of tanks where possible.[7]

Types and Features of Multiphase Pumps

Helico-Axial Pumps (Centrifugal) A rotodynamic pump with one single shaft requiring two mechanical seals. This pump utilizes an open-type axial impeller. This pump type is often referred to as a "Poseidon Pump" and can be described as a cross between an axial compressor and a centrifugal pump.

Twin Screw (Positive Displacement) The twin screw pump is constructed of two intermeshing screws that force the movement of the pumped fluid. Twin screw pumps are often used when pumping conditions contain high gas volume fractions and fluctuating inlet conditions. Four mechanical seals are required to seal the two shafts.

Progressive Cavity Pumps (Positive Displacement) Progressive cavity pumps are single-screw types typically used in shallow wells or at the surface. This pump is mainly used on surface applications where the pumped fluid may contain a considerable amount of solids such as sand and dirt.

Electric Submersible Pumps (Centrifugal) These pumps are basically multistage centrifugal pumps and are widely used in oil well applications as a method for artificial lift. These pumps are usually specified when the pumped fluid is mainly liquid.

Buffer Tank A buffer tank is often installed upstream of the pump suction nozzle in case of a slug flow. The buffer tank breaks the energy of the liquid slug, smoothes any fluctuations in the incoming flow and acts as a sand trap.

As the name indicates, multiphase pumps and their mechanical seals can encounter a large variation in service conditions such as changing process fluid composition, temperature variations, high and low operating pressures and exposure to abrasive/erosive media. The challenge is selecting the appropriate mechanical seal arrangement and support system to ensure maximized seal life and its overall effectiveness.[7][8][9]

Specifications

Pumps are commonly rated by horsepower, flow rate, outlet pressure in feet (or metres) of head, inlet suction in suction feet (or metres) of head. The head can be simplified as the number of feet or metres the pump can raise or lower a column of water at atmospheric pressure.

From an initial design point of view, engineers often use a quantity termed the specific speed to identify the most suitable pump type for a particular combination of flow rate and head.

Pumping power

The power added to the fluid flow by the pump (Po), is defined using SI units by:

 P_o=\rho\ g\ H\ Q

where:

Po is the output power of the pump (W)
ρ is the fluid density (kg/m3)
g is the gravitational constant (9.81 m/s2)
H is the energy Head added to the flow (m)
Q is the flow rate (m3/s)

Power is more commonly expressed as kW (103 W) or horsepower (multiply kW by 0.746), H is equivalent to the pressure head added by the pump when the suction and discharge pipes are of the same diameter. The power required to drive the pump is determined by dividing the output power by the pump efficiency

Power needed to pump a given flow against a given head and pipe size, can be calculated using this spread sheet.[10]

Various aspects of pumping energy usage are covered in "Energy Efficiency in Pumping".[11] Energy is consumed by the pump, and also lost in the pipework and these must be considered.

Pump efficiency

Pump efficiency is defined as the ratio of the power imparted on the fluid by the pump in relation to the power supplied to drive the pump. Its value is not fixed for a given pump, efficiency is a function of the discharge and therefore also operating head. For centrifugal pumps, the efficiency tends to increase with flow rate up to a point midway through the operating range (peak efficiency) and then declines as flow rates rise further. Pump performance data such as this is usually supplied by the manufacturer before pump selection. Pump efficiencies tend to decline over time due to wear (e.g. increasing clearances as impellers reduce in size).

One important part of system design involves matching the pipeline headloss-flow characteristic with the appropriate pump or pumps which will operate at or close to the point of maximum efficiency. There are free tools that help calculate head needed and show pump curves including their Best Efficiency Points (BEP).[12]

Pump efficiency is an important aspect and pumps should be regularly tested. Thermodynamic pump testing is one method.

See also

References

Further reading

  • Australian Pump Manufacturers' Association. Australian Pump Technical Handbook, 3rd edition. Canberra: Australian Pump Manufacturers' Association, 1987. ISBN 0731670434.
  • Hicks, Tyler G. and Theodore W. Edwards. Pump Application Engineering. McGraw-Hill Book Company.1971. ISBN 07-028741-4
  • Robbins, L. B. "Homemade Water Pressure Systems". Popular Science, February 1919, pages 83–84. Article about how a homeowner can easily build a pressurized home water system that does not use electricity.

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

PUMP, 1 a machine which drives a liquid from one point to another, generally at different levels, the latter being usually the higher; an air-pump is an appliance for exhausting or I The word appears apparently first in English in the Promptorium Parvulorum, c. 1440, of a ship's pump (hauritorium), in Dutch (pompe), a little later, dialectically, of a conduit pipe for water, but in the sense of a means of raising water it does not occur in Dutch or Ger. before the 16th century. The Fr. pompe is derived from Teut. The Ger. variant of Pumpe is Plumpe, which is generally taken as being an echoic word, imitating the sound of the plunger, but the primary notion seems to be that of a pipe or tube. Cf. Ital. term, tromba, i.e. trumpet, pipe (see the note on the word in the New English Dictionary). removing the air or other gas from a vessel, whilst a compression pump compresses the air. The simplest forms of pumps employed for forcing liquids are "plunger pumps," consisting essentially of a piston moving in a cylinder, provided with inlet and outlet pipes, together with certain valves. The 'disposition of these valves divides this type of pump into suction pumps and force pumps.

Fig. i shows the arrangement in a suction pump. A is the cylinder within which the piston B is moved up and down by the rod C. D is the inlet pipe (the lower extremity of which is placed beneath the surface of the liquid to be G removed), and G is the outlet pipe. E is a valve in the inlet pipe opening into the cylinder; and A the piston is perforated by one or more holes, each fitted with valves opening outwards on its upper surface. On raising the piston, the valve F remains closed and a vacuum tends to be created in the cylinder, but the pressure of the atmosphere forces the liquid up the tube D and it raises the valve E and passes into the cylinder. On reversing the motion the valve E closes and the liquid is forced through the valve F to the upper part of the cylinder. On again raising the piston, more liquid enters the lower part of the cylinder, whilst the previously raised liquid is ejected from the delivery pipe. Obviously the action is intermittent. Moreover, the height of the lift is conditioned by the atmospheric pressure, for this is the driving force; and since this equals 34 ft. of water, the lift cannot be theoretically more than this distance when water is being pumped.

In practice it may be considerably less, owing to leakage at the valves and between the piston and cylinder.

In the force pump (fig. 2) there is no such limitation to the lift.

In this case the piston is solid, and the outlet pipe, G which is placed at the bottom of the cylinder, has a valve F opening outwards, the inlet pipe and valve are the same as before. On raising the piston the liquid rises in the cylinder, the valve E opening and F remaining shut. On reversing the motion the - I valve E closes and the liquid is IL driven past the valve F. On again F J J raising the piston the valve E opens ?g G admitting more liquid whilst F re- mains closed. It is seen that the action is intermittent, liquid only being discharged during a down stroke, but since the driving force is that which is supplied to the piston rod, the lift is only con ditioned by the power available and by the strength of the pump. A continuous supply can be obtained by leading the delivery pipe into the base of an air chamber H, which is fitted with a discharge pipe J of such a diameter that the liquid cannot escape from it as fast as it is pumped in during a down stroke. The air inside is compressed in consequence and during an upstroke of the piston this air tends to regain its original volume and so expels the water, thus bringing about a continuous supply. For a description of modern pumps, see Hydraulics.

Air-pumps

Pumps for evacuating vessels may be divided into three classes: (i) mechanical, (2) mercurial, and (3) jet pumps; the last named are treated in Hydraulics.

The invention of the mechanical air-pump is generally attributed to Otto von Guericke, consul of Magdeburg, who exhibited his instrument in 1654; it was first described in 1657 by Gaspar Schott, professor of mathematics at Wurttemberg, in his NI echanica hydraulico-pneumatica, and afterwards (in 1672) by Guericke in his Experimenta nova Magdeburgica de vacus spatia. It consisted of a spherical glass vessel opening below by means of a stop-cock and narrow nozzle into the cylinder of an "exhausting syringe," which inclined upwards from the extremity of the nozzle. The cylinder, in which a well-fitting piston worked, was provided at its lower end with two valves. One of these opened from the nozzle into the cylinder, the other from the cylinder into the outside air. During the down-stroke of the piston the former was pressed home, so that no air entered the nozzle and vessel, while the latter was forced open by the air which so escaped from the cylinder. During the returnstroke the latter was kept closed in virtue of the partial vacuum formed within the cylinder, while at the same time the former n'as forced open by the pressure of the denser air in the vessel and nozzle. Thus, at every complete stroke of the piston, the air in the vessel or receiver was diminished by that fraction of itself which is expressed by the ratio of the volume of the available cylindrical space above the outward opening valve to the whole volume of receiver, nozzle and cylinder. The action is essentially that -of the common suction pump. The construction was subsequently improved by many experimenters, notably by Boyle, Hawksbee, Smeaton and others; and more recently two pump barrels were employed, so obtaining the same degree of exhaustion much more rapidly. This type of pump is, however, not very efficient, for there is not only leakage about the valves and between the piston and cylinder, but at a certain degree of exhaust the air within the vessel is insufficient to raise the inlet valve; this last defect has been met in some measure by using an extension of the piston to open and close the valve.

The so-called oil air-pumps are much more efficient; the valve difficulty is avoided, and the risk of leakage minimized; whilst in addition there is no air clearance between the piston and the base of the cylinder as in the older mechanical forms. The Fleuss pump may be taken as an example. The piston, provided with a valve opening upwards, is packed in the cylinder by a leather cup which is securely pressed against the sides of the cylinder by the atmospheric pressure. The piston rod passes through a valve in the upper part of the cylinder which is held to its seat by a spring. The inlet pipe enters an elliptical vessel which communicates with the cylinder a little way up from its base, whilst at the base there is a relief tube leading into the elliptical vessel already mentioned. Oil is placed both above the upper valve seating, and also in the cylinder up to the height of the lower edge of the inlet pipe. The action is as follows: On raising the piston it cuts off communication with the inlet pipe and then compresses the air above, forcing it through the upper valve and oil into the atmosphere. Some of the oil is also driven out, but as the valve does not close until the piston has descended a short distance, a certain amount of oil returns. On lowering the piston its valve opens and air passes in from the vessel to be exhausted; this is further rarefied on the next stroke and so on. The Max Kohl pumps are based on the same principle, but are constructed with more elaborate detail, leading to a greater efficiency, an exhaust of o 0008 mm. being claimed as readily obtainable.

The invention of the barometer and Torricelli's explanation of the vacuity above the mercury column placed before the members of the Florentine academy a ready method of obtaining vacua; for to exhaust a vessel it was only necessary to join, by means of a tube provided with stopcocks, the vessel to a barometer tube, fill the compound vessel with mercury and then to invert it in a basin containing this liquid, whereupon the mercury column fell, leaving a Torricellian vacuum in the vessel, which could be removed after shutting off the stop-cocks. This was the only method known until the invention of the mechanical air-pumps; it was subsequently employed by Count Rumford, and as late as 1845, Edward A. King patented filament electric lamps exhausted by the same methods. Although modern mercurial pumps have assumed a multiplicity of forms, their actions can be reduced to two principles, one statical, the other hydrodynamical - at the same time instruments have been devised utilizing both these principles.

Statical Pumps

The earliest mercurial pump, devised by Swedenborg and described in his Miscellanea observata circa yes naturales (1722), was statical in action, consisting essentially in replacing the solid piston of the mechanical pump by a column of mercury, which by being alternately raised and lowered gradually exhausted a vessel. A more complicated pump, but of much the same principle, was devised in 1784 by Joseph Baader, to be improved by C. F. Hindenburg in 1787, by A. N. Edelcrantz in 1804 and by J. H. Patten in 1824; whilst in 1881 Rankine Kennedy resuscitated the idea for the purpose of exhausting filament electric lamps. The pump devised by D FIG. I.

A H FIG. 2.

H. Geissler of Bonn, and first described in 1858 by W. H. Theo. Meyer in a pamphlet Ueber das geschichtete electrische Licht surpassed all previous forms in both simplicity and efficiency.

The general scheme of Geisler's pump is shown in fig. 3. A and B are pear-shaped glass vessels connected by a long narrow india-rubber tube, which must be sufficiently strong in the body (or strengthened by a linen coating) to stand an outward pressure of 1 to 2 atmospheres. A terminates below in a narrow vertical tube c which is a few inches longer than the height of the barometer, and to the lower end of this tube the india-rubber tube is attached which connects A with B. At the upper end of A is a glass two-way stop-cock, by turning which the vessel A can either be made to communicate with the vessel to be exhausted, or with the atmosphere, or can be shut off from both when the cock holds an intermediate position. The apparatus, after having been carefully cleaned and dried, is charged with pure and dry mercury which must next be worked backwards and forwards between A and B to remove all the air-bells. The air is then driven out of A by FIG. 3. lifting B to a sufficient level, turning the cock Geisler's Air-Pump. so as to communicate with the atmosphere and letting the mercury flow into A until it gets to the other side of the stop-cock, which is then placed in the intermediate position. Supposing the vessel to be exhausted to have already been securely connected to the pump, we now lower the reservoir B so as to reduce the pressure in A sufficiently below the tension in the gas to be sucked in, and, by turning the cock so as to connect A with the vessels to be exhausted, cause the gas to expand into and almost fill A. The cock is now shut against both communications, the reservoir lifted, the gas contents of A discharged and so on, until, when after an exhaustion mercury is let into A, the metal strikes against the top without interposition of a gas-bell. In a well-made apparatus the pressure in the exhausted vessel is now reduced to I t o or 2 1, of a millimetre, or even less. An absolute vacuum cannot be produced on account of the unavoidable air-film between the mercury and the walls of the apparatus.

As it takes a height of about 30 in. of mercury to balance the pressure of the atmosphere, a Geisler pump necessarily is a somewhat long-legged and unwieldy instrument; in addition, the long tube is liable to breakage. It can be considerably shortened, the two vessels A and B brought more closely together, and the somewhat objectionable india-rubber tube be dispensed with, if we connect the air-space in B with an ordinary air pump, and by means of it do the greater part of the sucking and the whole of the lifting work. An instrument thus modified was constructed by Poggendorff in 1865.

Even a Geisler's stop-cock requires to be lubricated to be absolutely gas-tight, and this occasionally proves a nuisance. Hence a number of attempts have been made to do without stop-cocks altogether. In the pump generally attributed to Topler, but which was previously devised by J. Mile of Warsaw in 1828, who termed it a "hydrostatic air-pump without cylinders, taps, lids or stoppers," this is attained by using, both for the inlet and the outlet, vertical capillary glass tubes, soldered, the former to somewhere near the bottom, the latter to the top of the vessel. These tubes, being more than 30 in. high, obviously act as efficient mercury-traps; but the already considerable height of the pump is thus multiplied by two. This consideration led Alexander Mitscherlich, F. Neisen and others to introduce glass valves in lieu of stop-cocks. A pump similar to Tdpler's construction was devised by Mendeleeff, and the original device has been much improved by Wiedemann, BesselHagen and others.

The best-known pump of this type was invented in 1865 by H. Sprengel, although the idea had been previously conceived by Magnus and Buff. The instrument, in its original (simplest) form (fig. 4), consists of a vertical capillary Pump. glass tube a of about 1 mm. bore, provided with a lateral branch b near its upper end, which latter, by an india-rubber joint governable by a screw-clamp, communicates with a funnel. The lower end is bent into the shape of a hook, and dips into a pneumatic trough. be exhausted is attached to b, and, in order to extract its gas contents, a properly regulated stream of mercury is allowed to fall through the vertical tube. Every drop of mercury, as it enters from the funnel, entirely closes the narrow tube like a piston, and in going past the place where the side tube enters entraps a portion of air and carries it down to the trough, where it can be collected. If the vertical tube, measuring from the point where the branch comes in, is a few inches greater than the height of the barometer, and the glass and mercury are perfectly clean, the apparatus slowly but surely produces an almost absolute vacuum.

The great advantages of Sprengel's pump lie in the simplicity of its construction and in the readiness with which it adapts itself to the collecting of the gas. It did excellent service in the hands of Graham for the extraction of gases occluded in metals. Many improvements upon the original construction have been FIG. 4.

proposed. Sprengel's Air-Pump.

Many other devices have been introduced for facilitating the production of vacua. For example Raps in 1893 described an automatic arrangement to be used in connexion with a Tdpler pump; whilst in 1893 Schulze-Berge devised a rotary form. For the description of these forms see Winkelmann, Handbuch der Physik (1906), i. 1316. The history of mercurial pumps is treated by S. P. Thompson, The Development of the Mercurial Air Pump (1888). For the production of high vacua, see Vacuum Tube; Liquid Gases.


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Wiktionary

Up to date as of January 15, 2010
(Redirected to pump article)

Definition from Wiktionary, a free dictionary

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English

Pronunciation

Etymology 1

From Middle English pumpe; compare German pumpen and Dutch pompen

Noun

Singular
pump

Plural
pumps

pump (plural pumps)

  1. A device for moving or compressing a liquid or gas.
    This pump can deliver 100 gallons of water per minute.
  2. An instance of the action of a pump; one stroke of a pump; any action similar to pumping
    It takes thirty pumps to get 10 litres ; he did 50 pumps of the weights.
  3. A device for dispensing liquid or gas to be sold, particularly fuel.
    This pump is out of order, but you can gas up at the next one.
  4. (bodybuilding) A swelling of the muscles caused by increased blood flow following high intensity weightlifting.
  5. (colloquial) A ride on a bicycle given to a passenger, usually on the handlebars or fender.
    She gave the other girl a pump on her new bike.
  6. (US, obsolete, slang) The heart.
Translations

Etymology 2

This definition is lacking an etymology or has an incomplete etymology. You can help Wiktionary by giving it a proper etymology.

Noun

Singular
pump

Plural
pumps

pump (plural pumps)

  1. (British) A type of shoe, a trainer or sneaker.
  2. (chiefly North American) A type of very high-heeled shoe; stilettoes.
    She was wearing a lovely new pair of pumps.
References
  • [1] Some images.
Synonyms
Translations

Etymology 3

Compare Dutch pompen and German pumpen

Verb

Infinitive
to pump

Third person singular
pumps

Simple past
pumped

Past participle
pumped

Present participle
pumping

to pump (third-person singular simple present pumps, present participle pumping, simple past and past participle pumped)

  1. (transitive) To use a pump to move (liquid or gas).
    I've pumped over 1000 gallons of water in the last ten minutes.
  2. (transitive) (often followed by up) To fill with air.
    He pumped up the air-bed by hand, but used the service station air to pump up the tyres.
  3. (transitive) To move rhythmically, as the motion of a pump.
    I pumped my fist with joy when I won the race.
  4. (transitive) To shake (a person's hand) vigorously.
  5. (transitive) To gain information from (a person) by persistent questioning.
  6. (intransitive) To use a pump to move liquid or gas.
    I've been pumping for over a minute but the water isn't coming through.
  7. (intransitive) (slang) To be going very well.
    The waves were really pumping this morning.
    Last night's party was really pumping.
Translations

Derived terms


Welsh

Etymology

From Proto-Indo-European *pénkʷe.

Pronunciation

Cardinal number

pump (before nouns pum)

  1. (cardinal) five

Simple English

[[File:|thumb|right|200px|A hand-pump]] A pump is a machine which moves a liquid or a gas from one place to another, often upwards. There are many different kinds of pumps. Pumps need some kind of power to make them work. Sometimes the power comes from a person. Sometimes the power comes from a motor.

File:Metering pump
Drawing of the inside of a metering pump head to show how it works. The piston moves back and forth inside the pump head.
bjn:Kumpa







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