High vacuum pumps are machines that create a high vacuum in an enclosed space. A perfect vacuum is a space in which no matter is present. No perfect vacuums exist, and it is impossible to create one. However, industrial vacuum pumps can create varying levels of atmospheric evacuation (the removal of air) in spaces, and high vacuum pumps can achieve very low levels of pressure.
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High vacuum pumps are used in many processes and create the conditions in which thousands of common products are manufactured. Vacuum pumps aid in the production of electric lamps and vacuum tubes that are found in microwaves and other appliances. In vehicles they enable hydraulic brakes and the function of cruise control; they power gyroscopes in various flight instruments for aircraft. Vacuum pumps are useful in medical applications like radiotherapy and suction tools and are also used in the fields of science and engineering for semiconductor and electron microscope work. There are three main categories of vacuum pumps: positive displacement, momentum transfer and entrapment pumps. High vacuums are usually created through the use of momentum transfer pumps. Diffusion and turbomolecular pumps, which are varieties of momentum transfer pumps, accelerate the molecules using high-speed gas jets or a series of high-speed fans to expel them from the sealed chamber.
There is a wide variety of high vacuum pump designs due to the many different applications and uses, though all pumps require a vacuum chamber, fittings, flanges, nozzles, intake valves and exhaust tubes. Many vacuum pump surfaces are electropolished to eliminate seams or pits where molecules can be trapped. Atmospheric pressure affects the properties of every material, so any rubber or plastic gaskets must be of the highest durability and strength. Vacuum surfaces are often baked to remove absorbed gases such as water or oils. Series or systems of pumps are often used to maximize pumping speed and effectiveness, and additional pumps can force evacuated gasses out of the enclosure and tubing. The two most common kinds of momentum transfer vacuum pumps, diffusion and turbomolecular, work by causing the gas molecules to accelerate through repeated collisions with a solid surface. This gives them momentum and allows the molecules to be steered out of the vacuum chamber. Turbomolecular pumps contain multiple levels of angled and rotating blades that direct evacuated molecules through a chamber while diffusion pumps use high speed jets of silicone oil to catch the gas molecules. The evacuated molecules cannot diffuse through the stream of oil and are carried out to the exhaust.
