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Vacuum Pump

admin — Fri, 26 Oct 2007 17:40:52 +0000

The ordinary vacuum pump was invented in 1650 by Otto von Guericke.

A vacuum pump is a pump that removes gas molecules from a sealed area in order to leave behind a partial vacuum.

Different pump types differ in details like sealing material, pressure, flow, manufacturing tolerances, tolerance to chemicals and dust and their tolerance to liquids and vibrations.

There are 3 main types of vacuum pumps:

The positive placement pump
The momentum transfer pump
The Entrapment pump

See also

Positive placement pump

admin — Fri, 26 Oct 2007 17:40:33 +0000

The positive placement pump uses a mechanism that repeatedly expands a cavity.
This is to allow gases to flow in from the chamber, seals off the cavity and exhausts the gas out to the atmosphere;

Positive displacement pumps are ideal for low vacuums but they tend to be ineffective in high vacuums.

Momentum transfer pump

The momentum transfer pump uses high speed jets of dense fluid or high speed rotating blades.

This is to knock gaseous molecules out of the chamber.

Momentum transfer pumps placed in series with positive displacement pumps are the most common configuration in the achievement of high vacuums but they often stall at low vacuums.

Entrapment pump

The entrapment pump that captures gases in a solid or absorbed state.
This type includes cryopumps, getters and ion pumps.

Entrapment pumps can be added in series to other types of pumps in order to reach ultra high vacuum states but they do not exhaust materials so their operational time is limited. Entrapment pumps periodically saturate and require regeneration, which generally means bringing the system up to higher temperatures and pressures.

Pump Performance Measures

admin — Fri, 26 Oct 2007 17:40:15 +0000

The pumping speed is also known as the volume flow rate.
It is measured at the pump’s inlet in liters per second , cubic feet per minute, or cubic meters per hour.

The throughput refers to the pumping speed multiplied by the gas pressure at the inlet and is measured in torr-liters/second and similar units.

The throughput is related to any vacuum leaks and refers to the volume leak rate multiplied by the pressure at the vacuum end of the leak.

The leak throughput can be compared to the pump throughput. The base pressure refers to the drop in the pumps mass flow to the same level as the mass flow in the chamber and represents a constant pressure.

The evaporation into a vacuum is called outgassing. The most common source of this is the water absorbed by materials in the chamber. At some point, the vacuum will approach the pump’s ultimate pressure or the best vacuum that this type of pump can achieve under ideal situations.

Adding more pumps in parallel or bigger pumps of the same type can still improve the pump-down speed but they will not reduce the base pressure below the ultimate. This is where better pumping technologies must be used to go beyond this barrier.