Vacuum pump
[2] Arabic engineer Al-Jazari later described dual-action suction pumps as part of water-raising machines in the 13th century.
[3][4][5] By the 17th century, water pump designs had improved to the point that they produced measurable vacuums, but this was not immediately understood.
[6] Other scientists took up the challenge, including Gasparo Berti, who replicated it by building the first water barometer in Rome in 1639.
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.
Robert Boyle improved Guericke's design and conducted experiments on the properties of vacuum.
[10] Heinrich Geissler invented the mercury displacement pump in 1855[10] and achieved a record vacuum of about 10 Pa (0.1 Torr).
Entrapment pumps can be added to reach ultrahigh vacuums, but they require periodic regeneration of the surfaces that trap air molecules or ions.
To continue evacuating a chamber indefinitely without requiring infinite growth, a compartment of the vacuum can be repeatedly closed off, exhausted, and expanded again.
Inside the pump, a mechanism expands a small sealed cavity to reduce its pressure below that of the atmosphere.
The pump's cavity is then sealed from the chamber, opened to the atmosphere, and squeezed back to a minute size.
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.
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.
[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.
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.
Often, all of the surfaces exposed to the vacuum must be baked at high temperature to drive off adsorbed gases.
With these standard precautions, vacuums of 1 mPa are easily achieved with an assortment of molecular pumps.
[citation needed] Ultra-high vacuum generally requires custom-built equipment, strict operational procedures, and a fair amount of trial-and-error.
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 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.
[47][48][49][50] 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.
