First, a single-stage impeller, similar to the top row of blades in a turbomolecular pump ensures the highest possible pumping speed for the open area of the pump's inlet.
In the second stage a high speed rotor spins between two closely-spaced, inner- and outer-cylindrical walls with helical grooves facing the rotor. When the rotor's tangential velocity approaches that of the average gas molecule's velocity, momentum transfer causes flow toward the exhaust port. To assist that flow, the spiral grooves on the outer wall have a downward shape while the ones on the inner wall have an upward shape.
In the third stage, a dynamic seal allows the pump to operate with a high exhaust pressure.
The drag pump accepts continuous inlet pressures below 0.1 Torr and discharges with a foreline pressure of 10 to 40 Torr. The latter pressure indicates that diaphragm pumps, not normally suitable for backing high vacuum pumps, could work in some applications with drag pumps.
First, a single-stage impeller, similar to the top row of blades in a turbomolecular pump ensures the highest possible pumping speed for the open area of the pump's inlet.In the second stage a high speed rotor spins between two closely-spaced, inner- and outer-cylindrical walls with helical grooves facing the rotor. When the rotor's tangential velocity approaches that of the average gas molecule's velocity, momentum transfer causes flow toward the exhaust port. To assist that flow, the spiral grooves on the outer wall have a downward shape while the ones on the inner wall have an upward shape.In the third stage, a dynamic seal allows the pump to operate with a high exhaust pressure.The drag pump accepts continuous inlet pressures below 0.1 Torr and discharges with a foreline pressure of 10 to 40 Torr. The latter pressure indicates that diaphragm pumps, not normally suitable for backing high vacuum pumps, could work in some applications with drag pumps.
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