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Vacuum pump
Vacuum pump
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The Roots blower is one example of a vacuum pump

A vacuum pump is a type of pump device that draws gas particles from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke, and was preceded by the suction pump, which dates to antiquity.[1]

History

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Early pumps

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The predecessor to the vacuum pump was the suction pump. Dual-action suction pumps were found in the city of Pompeii.[2] Arabic engineer Al-Jazari later described dual-action suction pumps as part of water-raising machines in the 13th century. He also said that a suction pump was used in siphons to discharge Greek fire.[3] The suction pump later appeared in medieval Europe from the 15th century.[3][4][5]

Student of Smolny Institute Catherine Molchanova with vacuum pump, by Dmitry Levitzky, 1776

By the 17th century, water pump designs had improved to the point that they produced measurable vacuums, but this was not immediately understood. What was known was that suction pumps could not pull water beyond a certain height: 18 Florentine yards according to a measurement taken around 1635, or about 34 feet (10 m).[6] This limit was a concern in irrigation projects, mine drainage, and decorative water fountains planned by the Duke of Tuscany, so the duke commissioned Galileo Galilei to investigate the problem. Galileo suggested, incorrectly, in his Two New Sciences (1638) that the column of a water pump will break of its own weight when the water has been lifted to 34 feet.[6] Other scientists took up the challenge, including Gasparo Berti, who replicated it by building the first water barometer in Rome in 1639.[7] Berti's barometer produced a vacuum above the water column, but he could not explain it. A breakthrough was made by Galileo's student Evangelista Torricelli in 1643. Building upon Galileo's notes, he built the first mercury barometer and wrote a convincing argument that the space at the top was a vacuum. The height of the column was then limited to the maximum weight that atmospheric pressure could support; this is the limiting height of a suction pump.[8]

In 1650, Otto von Guericke invented the first vacuum pump.[9] Four years later, he conducted his famous Magdeburg hemispheres experiment, showing that teams of horses could not separate two hemispheres from which the air had been evacuated. Robert Boyle improved Guericke's design and conducted experiments on the properties of vacuum. Robert Hooke also helped Boyle produce an air pump that helped to produce the vacuum.

By 1709, Francis Hauksbee improved on the design further with his two-cylinder pump, where two pistons worked via a rack-and-pinion design that reportedly "gave a vacuum within about one inch of mercury of perfect."[10] This design remained popular and only slightly changed until well into the nineteenth century.[10]

19th century

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Tesla's vacuum apparatus, published in 1892

Heinrich Geissler invented the mercury displacement pump in 1855[10] and achieved a record vacuum of about 10 Pa (0.1 Torr). A number of electrical properties become observable at this vacuum level, and this renewed interest in vacuum. This, in turn, led to the development of the vacuum tube.[11] The Sprengel pump was a widely used vacuum producer of this time.[10]

20th century

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The early 20th century saw the invention of many types of vacuum pump, including the molecular drag pump,[10] the diffusion pump,[12] and the turbomolecular pump.[13]

Types

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Pumps can be broadly categorized according to three techniques: positive displacement, momentum transfer, and entrapment.[14][15][16] Positive displacement pumps use a mechanism to repeatedly expand a cavity, allow gases to flow in from the chamber, seal off the cavity, and exhaust it to the atmosphere. Momentum transfer pumps, also called molecular pumps, use high-speed jets of dense fluid or high-speed rotating blades to knock gas molecules out of the chamber. Entrapment pumps capture gases in a solid or adsorbed state; this includes cryopumps, getters, and ion pumps.[14][15]

Positive displacement pumps are the most effective for low vacuums. Momentum transfer pumps, in conjunction with one or two positive displacement pumps, are the most common configuration used to achieve high vacuums. In this configuration the positive displacement pump serves two purposes. First it obtains a rough vacuum in the vessel being evacuated before the momentum transfer pump can be used to obtain the high vacuum, as momentum transfer pumps cannot start pumping at atmospheric pressures. Second the positive displacement pump backs up the momentum transfer pump by evacuating to low vacuum the accumulation of displaced molecules in the high vacuum pump. Entrapment pumps can be added to reach ultrahigh vacuums, but they require periodic regeneration of the surfaces that trap air molecules or ions. Due to this requirement their available operational time can be unacceptably short in low and high vacuums, thus limiting their use to ultrahigh vacuums. Pumps also differ in details like manufacturing tolerances, sealing material, pressure, flow, admission or no admission of oil vapor, service intervals, reliability, tolerance to dust, tolerance to chemicals, tolerance to liquids and vibration.[14][15][16]

Positive displacement pump

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The manual water pump draws water up from a well by creating a vacuum that water rushes in to fill. In a sense, it acts to evacuate the well, although the high leakage rate of dirt prevents a high quality vacuum from being maintained for any length of time.
Mechanism of a scroll pump

A partial vacuum may be generated by increasing the volume of a container. To continue evacuating a chamber indefinitely without requiring infinite growth, a compartment of the vacuum can be repeatedly closed off, exhausted, and expanded again. This is the principle behind a positive displacement pump, for example the manual water pump. Inside the pump, a mechanism expands a small sealed cavity to reduce its pressure below that of the atmosphere. Because of the pressure differential, some fluid from the chamber (or the well, in our example) is pushed into the pump's small cavity. The pump's cavity is then sealed from the chamber, opened to the atmosphere, and squeezed back to a minute size.[14][16]

More sophisticated systems are used for most industrial applications, but the basic principle of cyclic volume removal is the same:[17][18]

The base pressure of a rubber- and plastic-sealed piston pump system is typically 1 to 50 kPa, while a scroll pump might reach 10 Pa (when new) and a rotary vane oil pump with a clean and empty metallic chamber can easily achieve 0.1 Pa.

A positive displacement vacuum pump moves the same volume of gas with each cycle, so its pumping speed is constant unless it is overcome by backstreaming.

Momentum transfer pump

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A cutaway view of a turbomolecular high vacuum pump

In a momentum transfer pump (or kinetic pump[16]), gas molecules are accelerated from the vacuum side to the exhaust side (which is usually maintained at a reduced pressure by a positive displacement pump). Momentum transfer pumping is only possible below pressures of about 0.1 kPa. Matter flows differently at different pressures based on the laws of fluid dynamics. At atmospheric pressure and mild vacuums, molecules interact with each other and push on their neighboring molecules in what is known as viscous flow. When the distance between the molecules increases, the molecules interact with the walls of the chamber more often than with the other molecules, and molecular pumping becomes more effective than positive displacement pumping. This regime is generally called high vacuum.[14][16]

Molecular pumps sweep out a larger area than mechanical pumps, and do so more frequently, making them capable of much higher pumping speeds. They do this at the expense of the seal between the vacuum and their exhaust. Since there is no seal, a small pressure at the exhaust can easily cause backstreaming through the pump; this is called stall. In high vacuum, however, pressure gradients have little effect on fluid flows, and molecular pumps can attain their full potential.

The two main types of molecular pumps are the diffusion pump and the turbomolecular pump. Both types of pumps blow out gas molecules that diffuse into the pump by imparting momentum to the gas molecules. Diffusion pumps blow out gas molecules with jets of an oil or mercury vapor, while turbomolecular pumps use high speed fans to push the gas. Both of these pumps will stall and fail to pump if exhausted directly to atmospheric pressure, so they must be exhausted to a lower grade vacuum created by a mechanical pump, in this case called a backing pump.[16]

As with positive displacement pumps, the base pressure will be reached when leakage, outgassing, and backstreaming equal the pump speed, but now minimizing leakage and outgassing to a level comparable to backstreaming becomes much more difficult.

Entrapment pump

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An entrapment pump may be a cryopump, which uses cold temperatures to condense gases to a solid or adsorbed state, a chemical pump, which reacts with gases to produce a solid residue, or an ion pump, which uses strong electrical fields to ionize gases and propel the ions into a solid substrate. A cryomodule uses cryopumping. Other types are the sorption pump, non-evaporative getter pump, and titanium sublimation pump (a type of evaporative getter that can be used repeatedly).[14][15]

Other types

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Regenerative pump

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Main article: Pump § Regenerative turbine pumps

Regenerative pumps utilize vortex behavior of the fluid (air). The construction is based on hybrid concept of centrifugal pump and turbopump. Usually it consists of several sets of perpendicular teeth on the rotor circulating air molecules inside stationary hollow grooves like multistage centrifugal pump. They can reach to 1×10−5 mbar (0.001 Pa)(when combining with Holweck pump) and directly exhaust to atmospheric pressure. Examples of such pumps are Edwards EPX [19] (technical paper [20]) and Pfeiffer OnTool™ Booster 150.[21] It is sometimes referred as side channel pump. Due to high pumping rate from atmosphere to high vacuum and less contamination since bearing can be installed at exhaust side, this type of pumps are used in load lock in semiconductor manufacturing processes.

This type of pump suffers from high power consumption(~1 kW) compared to turbomolecular pump (<100W) at low pressure since most power is consumed to back atmospheric pressure. This can be reduced by nearly 10 times by backing with a small pump.[22]

More examples

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Additional types of pump include the:

  • Venturi vacuum pump (aspirator) (10 to 30 kPa)
  • Steam ejector (vacuum depends on the number of stages, but can be very low)

Performance measures

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Pumping speed refers to the volume flow rate of a pump at its inlet, often measured in volume per unit of time. Momentum transfer and entrapment pumps are more effective on some gases than others, so the pumping rate can be different for each of the gases being pumped, and the average volume flow rate of the pump will vary depending on the chemical composition of the gases remaining in the chamber.[23]

Throughput refers to the pumping speed multiplied by the gas pressure at the inlet, and is measured in units of pressure·volume/unit time. At a constant temperature, throughput is proportional to the number of molecules being pumped per unit time, and therefore to the mass flow rate of the pump. When discussing a leak in the system or backstreaming through the pump, throughput refers to the volume leak rate multiplied by the pressure at the vacuum side of the leak, so the leak throughput can be compared to the pump throughput.[23]

Positive displacement and momentum transfer pumps have a constant volume flow rate (pumping speed), but as the chamber's pressure drops, this volume contains less and less mass. So although the pumping speed remains constant, the throughput and mass flow rate drop exponentially. Meanwhile, the leakage, evaporation, sublimation and backstreaming rates continue to produce a constant throughput into the system.[23]

Techniques

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Vacuum pumps are combined with chambers and operational procedures into a wide variety of vacuum systems. Sometimes more than one pump will be used (in series or in parallel) in a single application. A partial vacuum, or rough vacuum, can be created using a positive displacement pump that transports a gas load from an inlet port to an outlet (exhaust) port. Because of their mechanical limitations, such pumps can only achieve a low vacuum. To achieve a higher vacuum, other techniques must then be used, typically in series (usually following an initial fast pump down with a positive displacement pump). Some examples might be use of an oil sealed rotary vane pump (the most common positive displacement pump) backing a diffusion pump, or a dry scroll pump backing a turbomolecular pump. There are other combinations depending on the level of vacuum being sought.

Achieving high vacuum is difficult because all of the materials exposed to the vacuum must be carefully evaluated for their outgassing and vapor pressure properties. For example, oils, greases, and rubber or plastic gaskets used as seals for the vacuum chamber must not boil off when exposed to the vacuum, or the gases they produce would prevent the creation of the desired degree of vacuum. Often, all of the surfaces exposed to the vacuum must be baked at high temperature to drive off adsorbed gases.[24]

Outgassing can also be reduced simply by desiccation prior to vacuum pumping.[24] High-vacuum systems generally require metal chambers with metal gasket seals such as Klein flanges or ISO flanges, rather than the rubber gaskets more common in low vacuum chamber seals.[25] The system must be clean and free of organic matter to minimize outgassing. All materials, solid or liquid, have a small vapour pressure, and their outgassing becomes important when the vacuum pressure falls below this vapour pressure. As a result, many materials that work well in low vacuums, such as epoxy, will become a source of outgassing at higher vacuums. With these standard precautions, vacuums of 1 mPa are easily achieved with an assortment of molecular pumps. With careful design and operation, 1 μPa is possible.[citation needed]

Several types of pumps may be used in sequence or in parallel. In a typical pumpdown sequence, a positive displacement pump would be used to remove most of the gas from a chamber, starting from atmosphere (760 Torr, 101 kPa) to 25 Torr (3 kPa). Then a sorption pump would be used to bring the pressure down to 10−4 Torr (10 mPa). A cryopump or turbomolecular pump would be used to bring the pressure further down to 10−8 Torr (1 μPa). An additional ion pump can be started below 10−6 Torr to remove gases which are not adequately handled by a cryopump or turbo pump, such as helium or hydrogen.[citation needed]

Ultra-high vacuum generally requires custom-built equipment, strict operational procedures, and a fair amount of trial-and-error. Ultra-high vacuum systems are usually made of stainless steel with metal-gasketed vacuum flanges. The system is usually baked, preferably under vacuum, to temporarily raise the vapour pressure of all outgassing materials in the system and boil them off. If necessary, this outgassing of the system can also be performed at room temperature, but this takes much more time. Once the bulk of the outgassing materials are boiled off and evacuated, the system may be cooled to lower vapour pressures to minimize residual outgassing during actual operation. Some systems are cooled well below room temperature by liquid nitrogen to shut down residual outgassing and simultaneously cryopump the system.[26]

In ultra-high vacuum systems, some very odd leakage paths and outgassing sources must be considered. The water absorption of aluminium and palladium becomes an unacceptable source of outgassing, and even the absorptivity of hard metals such as stainless steel or titanium must be considered. Some oils and greases will boil off in extreme vacuums. The porosity of the metallic vacuum chamber walls may have to be considered, and the grain direction of the metallic flanges should be parallel to the flange face.[26]

The impact of molecular size must be considered. Smaller molecules can leak in more easily and are more easily absorbed by certain materials, and molecular pumps are less effective at pumping gases with lower molecular weights. A system may be able to evacuate nitrogen (the main component of air) to the desired vacuum, but the chamber could still be full of residual atmospheric hydrogen and helium. Vessels lined with a highly gas-permeable material such as palladium (which is a high-capacity hydrogen sponge) create special outgassing problems.[26]

Applications

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Vacuum pumps are used in many industrial and scientific processes, including:

In the field of oil regeneration and re-refining, vacuum pumps create a low vacuum for oil dehydration and a high vacuum for oil purification.[44]

A vacuum may be used to power, or provide assistance to mechanical devices. In hybrid and diesel engine motor vehicles, a pump fitted on the engine (usually on the camshaft) is used to produce a vacuum. In petrol engines, instead, the vacuum is typically obtained as a side-effect of the operation of the engine and the flow restriction created by the throttle plate but may be also supplemented by an electrically operated vacuum pump to boost braking assistance or improve fuel consumption. This vacuum may then be used to power the following motor vehicle components:[45] vacuum servo booster for the hydraulic brakes, motors that move dampers in the ventilation system, throttle driver in the cruise control servomechanism, door locks or trunk releases.

In an aircraft, the vacuum source is often used to power gyroscopes in the various flight instruments. To prevent the complete loss of instrumentation in the event of an electrical failure, the instrument panel is deliberately designed with certain instruments powered by electricity and other instruments powered by the vacuum source.[46]

Depending on the application, some vacuum pumps may either be electrically driven (using electric current) or pneumatically-driven (using air pressure), or powered and actuated by other means.[47][48][49][50]

Hazards

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Old vacuum-pump oils that were produced before circa 1980 often contain a mixture of several different dangerous polychlorinated biphenyls (PCBs), which are highly toxic, carcinogenic, persistent organic pollutants.[51][52]

See also

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References

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Bibliography

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Vacuum pump

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from Grokipedia
A vacuum pump is a device that removes gas molecules from a sealed to achieve a partial by reducing the below atmospheric levels, enabling controlled low-pressure environments for various processes. Vacuum pumps operate on principles of gas transfer or gas binding, where gas molecules are either mechanically displaced from the to an exhaust or captured and immobilized within the pump using physical, chemical, or means. Performance is characterized by pumping speed, typically measured in liters per second or cubic feet per minute, which indicates the of gas removed per unit time, and ultimate , the lowest achievable vacuum level. Pumps are broadly classified into gas transfer pumps, which continuously compress and expel gas, and gas capture pumps, which trap molecules for later removal or regeneration. Common gas transfer examples include rotary vane pumps for rough vacuum (down to about 10^{-3} mbar), blowers as boosters for higher throughput, and turbomolecular pumps for high and (below 10^{-7} mbar). Gas capture types encompass cryopumps, which condense gases on cold surfaces below 120 K, and sputter-ion pumps, which chemically bind molecules using ionized reactive materials like . These pumps are essential in applications ranging from industrial processes like thin-film deposition and to scientific research in particle accelerators and space simulation, where they maintain precise levels to minimize and enable molecular-level control. Modern designs often integrate with vacuum systems including chambers, valves, and gauges to handle gas loads from leaks, , and .

Fundamentals

Definition and Purpose

A vacuum pump is a device that removes gas molecules from a sealed volume to create a partial , thereby reducing the below atmospheric levels. This process lowers the molecular density within the enclosed space, enabling controlled environments distinct from ambient conditions. The fundamental purpose of a vacuum pump is to generate and sustain low-pressure conditions essential for diverse processes in , , and industrial applications. These include preventing atmospheric contamination in sensitive operations, such as thin-film deposition where reduced gas presence minimizes impurities. Vacuum pumps also facilitate via suction-based lifting systems that secure objects without physical contact. Furthermore, they support phenomena like at lower temperatures by decreasing external pressure to match the liquid's , as demonstrated in setups. At its core, a vacuum pump consists of an for gas , a central pumping mechanism to displace the gas, and an exhaust outlet for its removal from the system. This setup contrasts with compressors, which instead elevate gas pressure through compression for high-pressure needs, whereas vacuum pumps prioritize evacuation for sub-atmospheric regimes. Over time, vacuum pumps have progressed from rudimentary air pumps of the , designed for basic evacuation experiments, to advanced configurations achieving ultra-high vacuums in modern contexts.

Vacuum Scales and Units

A vacuum is defined as a condition where the pressure of a gas is reduced below , specifically below 1 atm or 101.325 kPa, with measurements typically expressed relative to standard . This reduction is quantified using pressure units such as the pascal (Pa), the SI base unit equivalent to 1 N/m²; , defined as the pressure required to support 1 mm of mercury at 0°C; millibar (mbar), where 1 mbar = 100 Pa; and microns of mercury (μm Hg), equivalent to 10^{-3} or 0.133322 Pa. Common conversions include 1 = 133.322 Pa and 1 mbar ≈ 0.750 . Vacuum levels are classified into ranges based on , which determine the flow regime and application suitability:
RangePressure Range ()
Low vacuum760 to 1
Medium vacuum1 to 10^{-3}
High vacuum10^{-3} to 10^{-7}
Below 10^{-7}
Extreme vacuumBelow 10^{-12}
These classifications align with standard vacuum technology frameworks, where pressures are often approximated in for historical and practical reasons, though Pa is preferred in scientific contexts. The mean free path represents the average distance a gas molecule travels between collisions with other molecules, which increases inversely with pressure as the density of gas particles decreases. In low vacuum, frequent collisions occur due to short mean free paths on the order of micrometers, transitioning to molecular flow in high and ultra-high vacuum where paths extend to centimeters or meters; for example, in air at 10^{-3} torr and room temperature, the mean free path is approximately 5 cm, illustrating the shift to collisionless transport. This concept is critical for understanding gas behavior in vacuum systems, as derived from kinetic theory where the path length λ is proportional to temperature and inversely proportional to pressure and molecular cross-section. Vacuum scales and units have limitations arising from their dependence on gas composition and temperature, as mean free path and pressure measurements vary with molecular size, velocity, and interaction properties. For instance, lighter gases like hydrogen exhibit longer mean free paths than heavier ones like CO₂ at the same pressure due to smaller collision cross-sections, and higher temperatures increase molecular speeds, further extending paths. Gauge calibrations often assume air or nitrogen, requiring corrections for other gases to ensure accuracy.

Historical Development

Early Innovations

The earliest conceptual foundations for vacuum technology trace back to ancient pneumatics, where Greek-Egyptian engineer Hero of Alexandria (c. 10–70 AD) explored the principles of air and pressure in his treatise Pneumatica. Hero described devices that inadvertently demonstrated partial vacuums, such as siphons and fountains relying on atmospheric pressure to draw fluids, and he explicitly discussed the possibility of voids, challenging the prevailing philosophical notion of horror vacui (nature's aversion to a vacuum). Although his attempts to produce a sustained artificial vacuum were unsuccessful, these experiments laid groundwork for understanding air's behavior under manipulation, including steam-driven mechanisms like the aeolipile—a rotating sphere powered by escaping steam from a boiler—which illustrated reactive forces akin to evacuation processes. A significant leap occurred in the mid-17th century with the invention of the first practical air pump by German engineer and physicist Otto von Guericke around 1650. Guericke's device employed a piston within a cylinder equipped with one-way valves to expel air, creating a partial vacuum in a sealed chamber. He famously demonstrated its efficacy in 1654 through the Magdeburg hemispheres experiment, where two large copper hemispheres were joined and evacuated; atmospheric pressure then required teams of horses—or up to 16 men on each side—to separate them once the air was removed. This piston-cylinder setup marked the initial mechanical means to generate and study vacuum conditions systematically. In 1658, English natural philosopher , collaborating with , refined Guericke's design into a more reliable instrument by incorporating improved valves and seals, allowing for repeated evacuations with greater control and less air leakage. This enhanced pump facilitated precise experiments, including replications and extensions of Evangelista Torricelli's 1643 , which relied on a natural above a mercury column; Boyle's apparatus enabled observations of phenomena like the compression of air and the behavior of flames in low-pressure environments. However, these early pumps were constrained by rudimentary materials, such as leather gaskets treated with wax and oils for sealing, which permitted persistent leaks and limited achievable vacuums to roughly 1–6 (compared to standard of 760 ). These innovations profoundly influenced the scientific community by igniting widespread curiosity in pneumatics and the properties of air, shifting paradigms from Aristotelian plenism toward empirical investigations of voids and pressure. Guericke's public demonstrations and Boyle's detailed publications, such as New Experiments Physico-Mechanicall (1660), promoted experimental philosophy and collaborative witnessing, fostering advancements in fields like optics and physiology while underscoring the pump's role as a cornerstone tool for 17th-century natural philosophy.

19th and 20th Century Advances

In the mid-19th century, significant progress in vacuum technology was marked by the invention of the Sprengel pump in 1865 by Hermann Sprengel, a liquid piston design that utilized mercury falling through a narrow tube to create a vacuum by displacing air. This pump achieved pressures around 5 × 10^{-4} torr, representing a substantial improvement over earlier designs and enabling more reliable high-vacuum experiments. The enhanced vacuums produced by the Sprengel pump facilitated applications in early spectroscopy, particularly through Geissler tubes—sealed glass tubes partially evacuated using similar mercury-based techniques—which allowed researchers to observe gas discharge spectra for elemental identification. In 1882, August Toepler developed the Toepler pump, an improved mercury displacement pump using a oscillating liquid column to achieve vacuums down to about 10^{-5} torr, which was crucial for early X-ray and cathode ray tube experiments. The late 19th century saw the emergence of rotary vane pumps, with an early design patented in 1874 by Charles C. Barnes featuring vanes on a rotor within a cavity to create displacement for evacuation. By the early 1900s, companies like Western Electric began employing these rotary mechanisms for industrial processes such as telephone component manufacturing and incandescent lamp production, achieving medium vacuums down to about 10^{-2} torr with later oil-sealed designs introduced around 1904. Entering the 20th century, Wolfgang Gaede invented the diffusion pump in 1915, employing high-speed jets of mercury vapor to entrain and direct gas molecules toward an exhaust, attaining high vacuums on the order of 10^{-6} without in the . This innovation, later adapted with oil fluids for safer operation, revolutionized high-vacuum generation and supported the widespread commercial adoption of vacuum pumps in electric lamps and vacuum tubes during the and , where consistent low pressures were essential for filament longevity and flow. Concurrently, Irving Langmuir advanced vacuum measurement in 1916 with the development of the hot-cathode ionization gauge, which quantified low pressures by measuring ion currents from gas ionized by a heated filament, extending reliable detection to 10^{-6} and beyond. Further milestones in the mid-20th century included the , invented in 1958 by W. Becker and developed further by others including Marsbed Hablanian in the late , through designs featuring high-speed spinning blades that imparted momentum to gas molecules for evacuation down to 10^{-9} . These pumps, with rotor speeds exceeding 20,000 rpm, offered oil-free high-vacuum performance ideal for sensitive applications like particle accelerators. advancements paralleled these inventions, transitioning from fragile and hazardous mercury in early pumps to durable metals for casings and synthetic oils with low vapor pressures—such as polyphenyl ethers introduced in the 1940s—for and rotary vane systems, enhancing efficiency, safety, and longevity in industrial settings.

Modern Developments

In the early , the development of microelectromechanical systems ()-based pumps marked a significant advancement in , enabling portable solutions for lab-on-chip devices through piezoelectric actuation. These pumps utilize micro diaphragm mechanisms with passive flap valves to generate negative pressures, achieving absolute pressures as low as 19.2 kPa in single-stage configurations and down to about mbar in multistage cascades for applications like portable gas analyzers and chip-scale sensors. This technology facilitated integration into compact analytical instruments, reducing size and power requirements compared to traditional pumps while supporting levels suitable for and microscale experiments. Advancements in cryogenic pumps during the focused on integrating to enhance performance in manufacturing, where contamination-free environments are critical. Cryo-Torr series cryopumps, for instance, employ closed-cycle to condense gases on cold surfaces, routinely attaining pressures of 10−1010^{-10} or lower, which supports processes like and thin-film deposition. These improvements in efficiency and reliability stemmed from optimized designs that minimized consumption and maintenance downtime, enabling sustained operation in production-scale cleanrooms. Sustainability efforts in vacuum pump design gained momentum post-2005 with the widespread adoption of oil-free scroll pumps, which eliminate the need for lubricating fluids and reduce environmental hazards associated with oil disposal. Models like the Leybold SCROLLVAC plus series feature spiral scroll mechanisms that provide oil-free operation with low ultimate pressures around 0.01 mbar and pumping speeds up to 30 m³/h, while incorporating variable-speed drives to optimize energy use by adjusting motor output to demand. Similarly, Pfeiffer Vacuum's HiScroll pumps integrate interior permanent magnet motors for up to 20% energy savings over conventional designs, minimizing heat generation and operational costs without compromising performance. Since the 2020s, integration of (AI) and sensors into vacuum pumps has enabled smart systems for real-time monitoring and , particularly in precision applications. These systems embed IoT-connected sensors to track parameters like , , and , using AI algorithms to detect anomalies and forecast failures, thereby extending pump lifespan by up to 30% in industrial settings. In high-tech fields such as , where is essential for stability, smart pumps from providers like Leybold ensure precise control and minimal downtime through remote diagnostics. Recent milestones highlight the practical impact of these innovations, including NASA's deployment of diaphragm-based vacuum pumps in the Perseverance rover's sample acquisition system, launched in 2021, to extract and stabilize geological samples for chemical analysis under Martian conditions. The global vacuum pump market has correspondingly expanded, surpassing $6.5 billion by 2025, driven by demand in semiconductors, , and .

Classification and Types

Positive Displacement Pumps

Positive displacement pumps operate by trapping a fixed volume of gas within a chamber and then reducing that volume to compress and expel the gas through an exhaust port, creating a without relying on continuous flow. This mechanism follows , where the pressure-volume product remains constant during the compression cycle (P₁V₁ = P₂V₂). Unlike other pump types, these devices capture discrete volumes of gas in repetitive cycles, making them ideal for achieving low to medium levels, typically in the rough vacuum regime from down to about 1 mbar. Common subtypes include reciprocating piston pumps, which use a linearly moving within a to draw in, trap, compress, and discharge gas; the displacement volume for a single stroke is given by V_d = π r² h, where r is the piston and h is the stroke length. Diaphragm variants of reciprocating pumps employ a flexible instead of a to avoid direct contact with corrosive or contaminated gases, achieving ultimate pressures of 0.5–50 and pumping speeds of 10–60 L/min. Rotary vane pumps feature an eccentric rotor with sliding vanes that extend to form seals against the housing, trapping and compressing gas as the rotor turns; they typically deliver pumping speeds of 1–1200 m³/h and ultimate pressures below 10⁻³ mbar in two-stage configurations. Rotary screw pumps utilize two intermeshing, counter-rotating screws to transport gas axially without metal-to-metal contact, often in oil-free designs, with pumping speeds up to 1200 m³/h and ultimate pressures around 10⁻³ mbar. These pumps generally offer pumping speeds ranging from 1 to 100 m³/h for standard and industrial models, with ultimate pressures between 10⁻² and 10⁻³ mbar, though higher speeds up to 1200 m³/h are possible in larger units. They provide high compression ratios, often exceeding 10⁵ when oil-sealed, and are tolerant to vapors and particulates when equipped with gas ballast features that prevent inside the pump. However, lead to mechanical wear, requiring regular , and oil-lubricated models can introduce through backstreaming vapors. Diaphragm pumps, for instance, are favored in settings for analytical instruments due to their dry, oil-free operation that maintains clean environments without risks.

Momentum Transfer Pumps

Momentum transfer pumps operate by imparting momentum to gas molecules through collisions with high-speed moving surfaces or vapor jets, directing the molecules toward the exhaust port in a preferential manner to achieve evacuation. This mechanism relies on molecular flow conditions where the of gas molecules exceeds the spacing between moving parts, ensuring directed transport without significant intermolecular collisions. Key subtypes include turbomolecular pumps, which feature turbine-like rotors with blades spinning at 36,000 to 90,000 RPM to collide with gas molecules and propel them axially toward the backing port. Molecular drag pumps utilize rotating disks or spiral channels that drag molecules along viscous flow paths, suitable for medium to high levels up to a base of 10^{-7} mbar. Diffusion pumps employ supersonic jets of heated oil vapor, typically reaching speeds of several hundred meters per second, to transfer momentum to gas molecules and sweep them downward through a jet stack. These pumps exhibit high pumping speeds, such as up to 10,000 l/s for in large turbomolecular models, and ultimate pressures ranging from 10^{-7} to 10^{-10} mbar, depending on the gas and system preparation. The , defined as the ratio of inlet to outlet pressure, is significantly higher for heavier gases (e.g., ~10^9 for versus ~10^3 for in turbomolecular pumps), reflecting the dependence on . Advantages of momentum transfer pumps include the potential for oil-free operation in magnetically suspended designs, enabling clean high-vacuum environments, and robust performance in ultra-high vacuum applications. However, they require a backing pump to handle forepressure, typically below 10^{-2} Torr, and are sensitive to particulate contamination that can damage high-speed components. Turbomolecular pumps, for example, are widely used simulation chambers to maintain low pressures during testing.

Entrapment Pumps

Entrapment pumps, also known as capture pumps, operate by trapping gas molecules on a solid surface through physical adsorption, chemical absorption, or , without any mechanical movement. This mechanism relies on the interaction of gas molecules with a specialized medium, where they are either physisorbed via van der Waals forces, chemisorbed through chemical bonding, or implanted into the material lattice. These pumps are particularly suited for achieving ultra-high and extreme vacuum levels, as they produce no backstreaming or from . Key subtypes include sorption pumps, getter pumps, and ion pumps. Sorption pumps utilize materials like zeolites or activated charcoal to adsorb gases, often enhanced by cooling to temperatures (77 K) for cryosorption, which increases the trapping efficiency for condensable vapors such as water and hydrocarbons. Getter pumps, such as sublimation pumps, employ reactive metals like that are evaporated or sputtered onto surfaces to chemically bind reactive gases like , oxygen, and . Ion pumps, particularly sputter-ion types, generate a plasma via high-voltage discharge (e.g., Penning configuration) to ionize gases, accelerating the ions to bombard a where they are either buried in the material or form getter layers, effectively pumping noble gases like and . These pumps achieve ultimate pressures in the range of 10^{-9} to 10^{-12} mbar, depending on the subtype and system configuration, with pumping speeds varying by gas type—for instance, high for in cryopumps (up to thousands of liters per second) but lower for . Capacity is inherently limited by the available surface area of the trapping medium, necessitating periodic regeneration through heating to desorb accumulated gases, which restores functionality but interrupts operation. Advantages include vibration-free operation, production of clean hydrocarbon-free vacuums, and compatibility with sensitive environments like systems. However, disadvantages encompass finite capacity, inability to provide continuous pumping without regeneration, and selectivity toward certain gases, making them unsuitable as standalone roughing pumps. A prominent example is the use of cryopumps in the (LHC) at , where cold surfaces in the beam pipes act as distributed cryopumps to maintain extreme vacuum levels by cryosorbing residual gases, minimizing beam interactions and supporting pressures below 10^{-10} mbar.

Specialized Types

Specialized types of vacuum pumps encompass hybrid designs and emerging innovations that address niche requirements, such as handling contaminated gases, achieving rough vacuums in corrosive environments, or operating in extreme conditions like space, where traditional mechanical pumps may falter. These pumps often combine elements of positive displacement, transfer, or dynamic principles to provide versatility beyond standard classifications, enabling applications in challenging industrial and scientific settings. Regenerative pumps, also known as peripheral or side-channel pumps, operate by utilizing an with vanes that impart multiple compressions to the gas per revolution, creating a regenerative flow path that enhances efficiency in low-pressure regimes. This design allows for continuous gas circulation through peripheral channels, achieving ultimate pressures down to approximately 300 mbar while maintaining pumping speeds in the range of 0.1 to 50 m³/h for small models. They offer advantages like oil-free operation and resistance to minor contamination, making them suitable for analytical instruments and small-scale vacuum systems. Liquid ring pumps function through a rotating partially submerged in a sealing liquid, typically , which forms a concentric ring under to create compression chambers that handle wet, dirty, or condensable gases without internal contact between . Single-stage models achieve ultimate vacuums of 25 to 33 mbar, while two-stage variants reach lower pressures around 10 mbar, with capacities up to 50 m³/h for niche applications involving corrosive vapors. Their self-priming nature and ability to tolerate liquid slugs provide corrosion resistance and reliability in environments with high humidity or particulates, such as chemical processing. Venturi or ejector pumps generate rough vacuum using the , where a high-velocity motive gas jet expands through a to entrain and evacuate process gas, achieving pressures from atmospheric down to about 10 mbar without . These hybrid systems excel in high-throughput scenarios with pumping speeds of 1 to 100 m³/h and are favored for their simplicity, lack of lubrication, and tolerance to abrasives. In chemical plants, ejectors facilitate and processes by handling explosive or corrosive streams reliably.

Operating Principles

Pumping Mechanisms

Vacuum pumps remove gas from a chamber by compressing it to a higher and expelling it, a process governed by for ideal gases under isothermal conditions, where PV=constantPV = \text{constant}. This compression reduces the volume of gas molecules, increasing their density until they can be discharged against . At lower pressures, the becomes dominant, describing molecular motion where the λ\lambda—the average distance traveled between collisions—is inversely proportional to and given by λ=kT2πd2p\lambda = \frac{kT}{\sqrt{2} \pi d^2 p}
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