Rotary compression
Encyclopedia
A rotary compression pump
works in cycles. Over each cycle a volume is created in contact with the cavity where pressure is to be lowered. By random motion, molecules from the vacuum pass into the volume created by the pump. This volume is then cut off from the cavity and compressed in contact with a one way valve. If the volume is compressed enough some of the molecules will pass through the valve.
The maximum efficiency of a rotary compression pump is the ratio between the volume in contact with the vacuum and the smallest contracted volume in contact with the valve. If the ratio is 1:1000 and the pump is exhausting to atmospheric pressure, the highest achievable vacuum is 1/1000 of atmospheric pressure. This corresponds to 0.76 Torr
or 101.3 Pa. This limitation makes rotary compression pumps very hard to construct if lower pressures than about 1 Torr is to be achieved. The simplicity of the process makes the rotary compression pump cheap and it is widely used as a low vacuum pump
or a fore pump to a diffusion pump
.
See also rotary vane pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
works in cycles. Over each cycle a volume is created in contact with the cavity where pressure is to be lowered. By random motion, molecules from the vacuum pass into the volume created by the pump. This volume is then cut off from the cavity and compressed in contact with a one way valve. If the volume is compressed enough some of the molecules will pass through the valve.
The maximum efficiency of a rotary compression pump is the ratio between the volume in contact with the vacuum and the smallest contracted volume in contact with the valve. If the ratio is 1:1000 and the pump is exhausting to atmospheric pressure, the highest achievable vacuum is 1/1000 of atmospheric pressure. This corresponds to 0.76 Torr
Torr
The torr is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimetre of mercury, i.e., a pressure of 1 torr is approximately equal to 1 mmHg...
or 101.3 Pa. This limitation makes rotary compression pumps very hard to construct if lower pressures than about 1 Torr is to be achieved. The simplicity of the process makes the rotary compression pump cheap and it is widely used as a low vacuum pump
Vacuum pump
A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke.- Types :Pumps can be broadly categorized according to three techniques:...
or a fore pump to a diffusion pump
Diffusion pump
Diffusion pumps use a high speed jet of vapor to direct gas molecules in the pump throat down into the bottom of the pump and out the exhaust. Presented in 1915 by Wolfgang Gaede and using mercury vapor, they were the first type of high vacuum pumps operating in the regime of free molecular flow,...
.
See also rotary vane pump
Rotary vane pump
A rotary vane pump is a positive-displacement pump that consists of vanes mounted to a rotor that rotates inside of a cavity. In some cases these vanes can be variable length and/or tensioned to maintain contact with the walls as the pump rotates. It was invented by Charles C...