Evacuation apparatus

Abstract

The present invention proposes an evacuation apparatus including a mechanical booster pump 5 , a back pump 3 placed at a down-stream side of the mechanical booster pump in series, the booster pump 5 having discharge openings 27 a and 27 b for discharging a low compression gas and a discharge opening 29 for discharging a high compression gas, and, in a stage where gas-discharging is started, the gas is discharged toward the ambient side through the discharge opening 29 for discharging a high compression gas with the operation of the mechanical booster pump and, in a stage where the discharged gas pressure reaches afterward a medium vacuum, the back pump starts operation and the gas is sent to the back pump through the discharge openings 27 a and 27 b for discharging a low compression gas.

1 . An evacuation apparatus for evacuating a tank, a chamber and the like, comprising a mechanical booster pump, a back pump placed at a down-stream side of the mechanical booster pump in series, and a controller for controlling operation of the apparatus; 
 wherein the mechanical booster pump has at least one discharge opening for discharging a low compression gas, through which lowly-compressed gas with low compression ratio on a part way of compression in the booster pump is emitted, and a discharge opening for discharging a high compression gas, through which highly-compressed gas with high compression ratio is emitted; and    wherein the controller controls so that, in a stage where gas-discharging is started, the gas is discharged toward the ambient side through the discharge opening for discharging a high compression gas with the operation of the mechanical booster pump and, in a stage where the discharged gas pressure reaches afterward a medium vacuum, the back pump starts operation and the gas is sent to the back pump through the discharge openings for discharging a low compression gas.    
   
   
       2 . An evacuation apparatus according to  claim 1 , wherein the controller recognizes the medium vacuum attained by means of an elapsed time detected by a timer.  
   
   
       3 . An evacuation apparatus according to  claim 1 , wherein the mechanical booster pump is a vacuum pump of a claw type, in which the discharge opening for discharging a high compression gas is located at a wall of the pump casing, the wall being in a plane vertical to the axes of the pump rotors, while the discharge opening for discharging a high compression gas faces the compression space, being located in a plane parallel to the plane containing both rotation axes of the pump rotors.