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Vacuum Pump Basics

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Bekijk de hele lijst. Vaak samen gekocht. David Keuning Groei en ontwikkeling van een bedrijf Tweedehands 15, 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. 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 can be reduced by nearly 10 times by backing with a small pump. 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.

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. 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. 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. 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.

Guide Industrial Vacuum 101 - Second Edition: The Basics of Vacuum Technology

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. Outgassing can also be reduced simply by desiccation prior to vacuum pumping. 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.

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.

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 Torr , kPa to 25 Torr 3 kPa. 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. 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.

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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. 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. In the field of oil regeneration and rerefining, vacuum pumps create a low vacuum for oil dehydration and a high vacuum for oil purification. 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 vacuum.

In petrol engines , instead, 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: [14] 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. Old vacuum-pump oils that were produced before circa often contain a mixture of several different dangerous polychlorinated biphenyls PCBs , which are highly toxic , carcinogenic , persistent organic pollutants.

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This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Mechanism of a scroll pump. Archived from the original on February 26, Retrieved Archived from the original on Hablanian In Rita G. Lerner; George L. Trigg eds. Encyclopedia of Physics Second ed.

VCH Publishers Inc. Pfeiffer Vacuum.