Vacuum pump

A vacuum pump is a pump that removes gas to leave behind a partial vacuum (of varying quality, depending on the pump). Various mechanisms can be used; sometimes more than one will be used (in series or in parallel) in a single application.

A partial 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 fairly crude partial vacuum. To achieve a more-perfect vacuum, other techniques must then be used (usually following an initial fast "pump down" using a positive displacement pump). In a turbomolecular pump, the momentum transfer principle is used, accelerating the gas molecules from the vacuum side to the exhaust side (which is usually maintained at a reduced pressure by a positive displacement pump). Another alternative is cryogenic entrapment where individual gas molecules are liquified and contained in a cold trap.

Achieving truly high vacuums is difficult because all of the materials exposed to the vacuum must be carefully evaluated for their outgassing properties. For example, oils, greases, rubber, or plastic used to form gaskets and sealss must not boil off when exposed to the vacuum or the gases they produced 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.

Types of vacuum pumps

• rubber and plastic-sealed piston pump (1 to 50 kPa)
• venturi vacuum pump (10 to 30 kPa)
• scroll pump (10 Pa)
• rotary vane oil pump (0.1 Pa)

• Transfer
• *roots blower
• *rotary compression
• *Diffusion pump
• *turbomolecular pump
• *Liquid Ring

• entrapment pump
• *ion pump
• *cryopump

  Uses of vacuum pumps

  
  Vacuum pumps are used in many industrial and scientific processes including:
• The production of most types of electric lamps, vacuum tubes, and CRTs where the device is either left evacuated or re-filled with a specific gas or gas mixture
• Semiconductor processing, notably ion implantation and sputtering
• Electron microscopy
• Medical processes that require suction