Editing Pump (section)

=== Positive-displacement pumps{{anchor|Positive-displacement pump}} ===
[[Image:LobePump en.svg|thumb|right|upright|[[Lobe pump]] internals]]

[[Image:LobePump3DAnimationArrows.gif|thumb|right|upright|[[Lobe pump]] internals]]

A positive-displacement pump makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe.

Some positive-displacement pumps use an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. The volume is constant through each cycle of operation.

==== Positive-displacement pump behavior and safety ====
Positive-displacement pumps, unlike [[Centrifugal pump|centrifugal]], can theoretically produce the same flow at a given rotational speed no matter what the discharge pressure. Thus, positive-displacement pumps are ''constant flow machines''. However, a slight increase in internal leakage as the pressure increases prevents a truly constant flow rate.

A positive-displacement pump must not operate against a closed valve on the discharge side of the pump, because it has no shutoff head like centrifugal pumps. A positive-displacement pump operating against a closed discharge valve continues to produce flow and the pressure in the discharge line increases until the line bursts, the pump is severely damaged, or both.

A relief or [[safety valve]] on the discharge side of the positive-displacement pump is therefore 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 is usually used only as a safety precaution.  An external relief valve in the discharge line, with a return line back to the suction line or supply tank, provides increased [[safety]].

==== Positive-displacement types ====
A positive-displacement pump can be further classified according to the mechanism used to move the fluid:

* ''Rotary-type'' positive displacement: internal and external [[gear pump]], [[screw pump]], [[lobe pump]], shuttle block, [[rotary vane pump|flexible vane and sliding vane]], circumferential piston, [[flexible impeller]], helical twisted roots (e.g. the Wendelkolben pump) and [[liquid-ring pump]]s
* ''Reciprocating-type'' positive displacement: [[piston pump]]s, [[plunger pump]]s and [[diaphragm pump]]s
* ''Linear-type'' positive displacement: [[rope pump]]s and [[chain pump]]s

===== '''Rotary positive-displacement pumps''' =====
[[File:Pompe à palettes.gif|thumb| [[Rotary vane pump]] ]]

These pumps move fluid using a rotating mechanism that creates a vacuum that captures and draws in the liquid.<ref>{{Cite news|url=http://www.pumpscout.com/articles-expert-advice/understanding-positive-displacement-pumps-aid89.html|title=Understanding positive displacement pumps {{!}} PumpScout|access-date=2018-01-03|archive-date=2018-01-04|archive-url=https://web.archive.org/web/20180104073336/http://www.pumpscout.com/articles-expert-advice/understanding-positive-displacement-pumps-aid89.html|url-status=dead}}</ref>

''Advantages:'' Rotary pumps are very efficient<ref>{{Cite web|url=https://www.pumpsandsystems.com/rotary-pumps/may-2015-volumetric-efficiency-rotary-positive-displacement-pumps|title=The Volumetric Efficiency of Rotary Positive Displacement Pumps|website=www.pumpsandsystems.com|access-date=2019-03-27|date=2015-05-21}}</ref> because they can handle highly viscous fluids with higher flow rates as viscosity increases.<ref>{{Cite web|url=http://www.lobepro.com/fund-why-choose-lobepro-12-reasons.php|title=Positive Displacement Pumps - LobePro Rotary Pumps|last=inc.|first=elyk innovation|website=www.lobepro.com|access-date=2018-01-03|archive-date=2018-01-04|archive-url=https://web.archive.org/web/20180104013854/http://www.lobepro.com/fund-why-choose-lobepro-12-reasons.php|url-status=dead}}</ref>

''Drawbacks:'' The nature of the pump requires very close clearances between the rotating pump and the outer edge, making it rotate at a slow, steady speed. If rotary pumps are operated at high speeds, the fluids cause erosion, which eventually causes enlarged clearances that liquid can pass through, which reduces efficiency.

Rotary positive-displacement pumps fall into five main types:
* [[Gear pump]]s – a simple type of rotary pump where the liquid is pushed around a pair of gears.
* [[Screw pump]]s – the shape of the internals of this pump is usually two screws turning against each other to pump the liquid
* [[Rotary vane pump]]s
* Hollow disc pumps (also known as eccentric disc pumps or hollow rotary disc pumps), similar to [[scroll compressor]]s, these have an eccentric cylindrical rotor encased in a circular housing. As the rotor orbits, it traps fluid between the rotor and the casing, drawing the fluid through the pump. It is used for highly viscous fluids like petroleum-derived products, and it can also support high pressures of up to 290 psi.<ref>{{Cite web|url=https://www.psgdover.com/mouvex/products/eccentric-disc-pumps|title=Eccentric Disc Pumps|website=PSG}}</ref><ref>{{Cite web|url=https://www.apexequipmentltd.com/omg-pumps/hollow-disc-rotary-pumps/|title=Hollow Disc Rotary Pumps|website=APEX Equipment|access-date=2019-12-20|archive-date=2020-08-06|archive-url=https://web.archive.org/web/20200806144704/https://www.apexequipmentltd.com/omg-pumps/hollow-disc-rotary-pumps/|url-status=dead}}</ref><ref>{{Cite web|url=http://www.mpompe.com/en/principi-funzionamento.html|title=M Pompe &#124; Hollow Oscillating Disk Pumps &#124; self priming pumps &#124; reversible pumps &#124; low-speed pumps|website=www.mpompe.com|access-date=2019-12-20|archive-date=2020-02-06|archive-url=https://web.archive.org/web/20200206090355/http://www.mpompe.com/en/principi-funzionamento.html|url-status=dead}}</ref><ref>{{Cite web|url=https://www.bedu.eu/products/hollow+disc+pumps|title=Hollow disc pumps|website=Pump Supplier Bedu}}</ref><ref>{{Cite web|url=https://www.3pprinz.com/product-3p-hollow-turbik-series.php?lang=en|title=3P PRINZ - Hollow rotary disk pumps - Pompe 3P - Made in Italy|website=www.3pprinz.com|access-date=2019-12-20|archive-date=2020-08-06|archive-url=https://web.archive.org/web/20200806122911/https://www.3pprinz.com/product-3p-hollow-turbik-series.php?lang=en|url-status=dead}}</ref><ref>{{Cite web|url=https://magnatexpumps.com/mobile/hollow-disc-pump.php|title=Hollow Disc Pump|website=magnatexpumps.com|access-date=2019-12-20|archive-date=2020-08-06|archive-url=https://web.archive.org/web/20200806125134/https://magnatexpumps.com/mobile/hollow-disc-pump.php|url-status=dead}}</ref><ref>{{Cite web|url=https://candyne.com/hollow-rotary-disc-pump/|title=Hollow Rotary Disc Pumps|date=November 4, 2014}}</ref>
* [[Peristaltic pump]]s have rollers which pinch a section of flexible tubing, forcing the liquid ahead as the rollers advance.  Because they are very easy to keep clean, these are popular for dispensing food, medicine, and [[Concrete pump|concrete]].

===== '''Reciprocating positive-displacement pumps''' =====
[[Image:Hand pump-en.svg|thumb|Simple hand pump]]
[[File:Old hand water pump.jpg|thumb|Antique "pitcher" pump (c. 1924) at the Colored School in Alapaha, Georgia, US]]
{{See also|Reciprocating pump}}
Reciprocating pumps move the fluid using one or more oscillating pistons, plungers, or membranes (diaphragms), while valves restrict fluid motion to the desired direction. In order for suction to take place, the pump must first pull the plunger in an outward motion to decrease pressure in the chamber. Once the plunger pushes back, it will increase the chamber pressure and the inward pressure of the plunger will then open the discharge valve and release the fluid into the delivery pipe at constant flow rate and increased pressure.

Pumps in this category range from ''simplex'', with one cylinder, to in some cases ''quad'' (four) cylinders, or more. Many reciprocating-type pumps are ''duplex'' (two) or ''triplex'' (three) cylinder. They can be either ''single-acting'' with suction during one direction of piston motion and discharge on the other, or ''double-acting'' with suction and discharge in both directions. The pumps can be powered manually, by air or steam, or by a belt driven by an engine. This type of pump was used extensively in the 19th century—in the early days of steam propulsion—as boiler feed water pumps. Now reciprocating pumps typically pump highly viscous fluids like concrete and heavy oils, and serve in special applications that demand low flow rates against high resistance. Reciprocating [[hand pump]]s were widely used to pump water from wells. Common [[bicycle pump]]s and foot pumps for [[Inflatable|inflation]] use reciprocating action.

These positive-displacement pumps have 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 and the pump's volumetric efficiency can be achieved through routine maintenance and inspection of its valves.<ref>{{Cite news|url=https://info.triangle-pump.com/blog/what-is-volumetric-efficiency|title=What Is Volumetric Efficiency?|last=Inc.|first=Triangle Pump Components|access-date=2018-01-03}}</ref>

Typical reciprocating pumps are:
* ''[[Plunger pump]]'' – a reciprocating plunger pushes the fluid through one or two open valves, closed by suction on the way back.
* ''[[Diaphragm pump]]'' – similar to plunger pumps, where 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.
* ''[[Piston pump]]'' displacement pumps'' – usually simple devices for pumping small amounts of liquid or gel manually. The common hand soap dispenser is such a pump.
* ''[[Radial piston pump]]''{{dash}}a form of hydraulic pump where pistons extend in a radial direction.
* Vibratory pump or vibration pump{{dash}}a particularly low-cost form of plunger pump, popular in low-cost [[espresso machine]]s.<ref>{{Cite web|url=https://www.home-barista.com/espresso-machines/faqs-and-favorites-t1541.html|title=FAQs and Favorites{{dash}}Espresso Machines|website=www.home-barista.com|date=21 November 2014 }}</ref><ref>{{Cite web|url=https://clivecoffee.com/blogs/learn/the-pump-the-heart-of-your-espresso-machine|title=The Pump: The Heart of Your Espresso Machine|website=Clive Coffee}}</ref>  The only moving part is a spring-loaded piston, the armature of a [[Solenoid (engineering)|solenoid]].  Driven by [[Rectified sine wave#Half-wave rectification|half-wave rectified]] [[alternating current]], the piston is forced forward while energized, and is retracted by the spring during the other half cycle.  Due to their inefficiency, vibratory pumps typically cannot be operated for more than one minute without overheating, so are limited to intermittent duty.

====='''Various positive-displacement pumps'''=====

The positive-displacement principle applies in these pumps:

* [[Lobe pump|Rotary lobe pump]]
* [[Progressing cavity pump]]
* [[Gear pump|Rotary gear pump]]
* [[Piston pump]]
* [[Diaphragm pump]]
* [[Screw pump]]
* [[Gear pump]]
* [[Hydraulic pump]]
* [[Rotary vane pump]]
* [[Peristaltic pump]]
* [[Rope pump]]
* [[Flexible impeller]]&nbsp;pump

======'''Gear pump'''======
[[Image:Gear pump.png|thumb|Gear pump]]
{{Main article|Gear pump}}

This is the simplest form of rotary positive-displacement pumps. It consists of two meshed gears that rotate in a closely fitted casing. The tooth spaces trap fluid and force it around the outer periphery. The fluid does not travel back on the meshed part, because the teeth mesh closely in the center.  Gear pumps see wide use in car engine oil pumps and in various [[hydraulic power pack]]s.
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======'''Screw pump'''======
[[Image:Lysholm screw rotors.jpg|thumb|upright|Screw pump]]
{{Main article|Screw pump}}

A [[screw pump]] is a more complicated type of rotary pump that uses two or three screws with opposing thread — e.g., one screw turns clockwise and the other counterclockwise. The screws are mounted on parallel shafts that often have gears that mesh so the shafts turn together and everything stays in place. In some cases the driven screw drives the secondary screw, without gears, often using the fluid to limit abrasion. The screws turn on the shafts and drive fluid through the pump. As with other forms of rotary pumps, the clearance between moving parts and the pump's casing is minimal.
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======'''Progressing cavity pump'''======
{{Main article|Progressing cavity pump}}

[[File:Progressive_cavity_pump_animation.gif|thumb|right|Progressing cavity pump]]

Widely used for pumping difficult materials, such as sewage sludge contaminated with large particles, a progressing cavity pump consists of a helical rotor, about ten times as long as its width, and a stator, mainly made out of rubber. This can be visualized as a central core of diameter ''x'' with, typically, a curved spiral wound around of thickness half ''x'', though in reality it is manufactured in a single lobe.  This shaft fits inside a heavy-duty rubber sleeve or stator, of wall thickness also typically ''x''. As the shaft rotates inside the stator, the rotor gradually forces fluid up the rubber cavity.  Such pumps can develop very high pressure at low volumes at a rate of 90 PSI per stage on water for standard configurations.
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======'''Roots-type pump'''======
[[image:lobbenpomp.gif|thumb|right|A Roots lobe pump]]
{{main article|Roots-type supercharger}}

Named after the Roots brothers who invented it, this [[lobe pump]] displaces the fluid trapped between two long helical rotors, each fitted into the other when perpendicular at 90°, rotating inside a triangular shaped sealing line configuration, both at the point of suction and at the point of discharge. This design produces a continuous flow with equal volume and no vortex. It can work at low [[:wikt:pulse|pulsation]] rates, and offers gentle performance that some applications require.

Applications include:
* High capacity [[gas compressor|industrial air compressors]].
* [[Roots supercharger]]s on [[internal combustion engine]]s.
* A brand of civil defense siren, the [[Federal Signal Corporation]]'s [[Thunderbolt siren|Thunderbolt]].

======'''Peristaltic pump'''======
[[Image:eccentric pump.gif|thumb|360° peristaltic pump]]
{{Main article|Peristaltic pump}}

A ''peristaltic pump'' is a type of positive-displacement pump. It contains fluid within a flexible tube fitted inside a circular pump casing (though linear peristaltic pumps have been made). A number of ''rollers'', ''shoes'', or ''wipers'' attached to a [[rotor (turbine)|rotor]] compress the flexible tube. As the rotor turns, the part of the tube under compression closes (or ''occludes''), forcing the fluid through the tube. Additionally, when the tube opens to its natural state after the passing of the cam it draws (''restitution'') fluid into the pump. This process is called ''[[peristalsis]]'' and is used in many biological systems such as the [[gastrointestinal tract]].
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======'''Plunger pumps'''======
{{Main article|Plunger pump}}

''Plunger pumps'' are reciprocating positive-displacement pumps.

These consist of a cylinder with a reciprocating plunger. 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.
Efficiency and common problems: With only one cylinder in plunger pumps, 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. Centrifugal pumps are also susceptible to water hammer. [https://theengineeringguide.com/all-articles/f/surge-analysis-a-vital-tool-for-safe-and-reliable-pipeline-opera Surge analysis], a specialized study, helps evaluate this risk in such systems.

======'''Triplex-style plunger pump'''======
Triplex plunger pumps use three plungers, which reduces the pulsation relative to single reciprocating plunger pumps.  Adding a pulsation dampener on the pump outlet can further smooth the ''pump ripple'', or ripple graph of a pump transducer. The dynamic relationship of the high-pressure fluid and plunger generally requires high-quality plunger seals. Plunger pumps with a larger number of plungers have the benefit of increased flow, or smoother flow without a pulsation damper. The increase in moving parts and crankshaft load is one drawback.

Car washes often use these triplex-style plunger pumps (perhaps without pulsation dampers). In 1968, William Bruggeman reduced the size of the triplex pump and increased the lifespan so that car washes could use equipment with smaller footprints. Durable high-pressure seals, low-pressure seals and oil seals, hardened crankshafts, hardened connecting rods, thick ceramic plungers and heavier duty ball and roller bearings improve reliability in triplex pumps.  Triplex pumps now are in a myriad of markets across the world.

Triplex pumps with shorter lifetimes are commonplace to the home user. A person who uses a home pressure washer for 10 hours a year may be satisfied with a pump that lasts 100 hours between rebuilds.  Industrial-grade or continuous duty triplex pumps on the other end of the quality spectrum may run for as much as 2,080 hours a year.<ref>{{Cite web|url=http://pressurewashr.com/pressure-washer-pumps/|title=Definitive Guide: Pumps Used in Pressure Washers|website=The Pressure Washr Review|date=13 August 2015 |access-date=May 14, 2016}}</ref>

The oil and gas drilling industry uses massive semi-trailer-transported triplex pumps called [[mud pump]]s to pump [[drilling mud]], which cools the drill bit and carries the cuttings back to the surface.<ref>
[http://www.gardnerdenverpumps.com/pumps/ "Drilling Pumps"].
[[Gardner Denver]].
</ref>
Drillers use triplex or even quintuplex pumps to inject water and solvents deep into shale in the extraction process called ''[[fracking]]''.<ref>
[http://www.gardnerdenverpumps.com/pumps/stimulation-fracturing/gd-2500/ "Stimulation and Fracturing pumps: Reciprocating, Quintuplex Stimulation and Fracturing Pump"] {{webarchive|url=https://web.archive.org/web/20140222144759/http://www.gardnerdenverpumps.com/pumps/stimulation-fracturing/gd-2500/ |date=2014-02-22 }}.
Gardner Denver.
</ref>

======'''Diaphragm pump'''======
Typically run on electricity compressed air, [[diaphragm pump]]s are relatively inexpensive and can perform a wide variety of duties, from pumping air into an [[aquarium]], to liquids through a [[filter press]]. Double-diaphragm pumps can handle viscous fluids and abrasive materials with a gentle pumping process ideal for transporting shear-sensitive media.<ref>{{Cite news|url=https://www.globalpumps.com.au/blog/advantages-of-an-air-operated-double-diaphragm-pump|title=Advantages of an Air Operated Double Diaphragm Pump|access-date=2018-01-03|language=en}}</ref>

======'''Rope pump'''======
[[File:Rope Pump.svg|thumb|Rope pump schematic]]
{{Main article|Rope pump}}

Devised in China as [[chain pump]]s over 1000 years ago, these pumps can be made from very simple materials: A rope, a wheel and a pipe are sufficient to make a simple rope pump. Rope pump efficiency has been studied by grassroots organizations and the techniques for making and running them have been continuously improved.<ref>[http://tanzaniawater.blogspot.com/2010/08/hi-its-cai.html Tanzania water] {{Webarchive|url=https://web.archive.org/web/20120331051643/http://tanzaniawater.blogspot.com/2010/08/hi-its-cai.html |date=2012-03-31 }} blog – example of grassroots researcher telling about his study and work with the rope pump in Africa.</ref>
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