A single-stage Alexander type oil diffusion pump (inside dia. 80mmø) has been constructed, and the variation of the characteristics was measured when the distance between the jet and the inclined wall (30° to the pumping direction) was altered.
When the distance is longer than a certain critical length, the true speed of the pump is fairly constant, but becomes gradually smaller when the distance is decreased below the limiting value. On the other hand, the back diffusion at first decreases on reducing the distance, but begins to increase when the distance is made shorter than the critical value mentioned above. Thus there is an optimum distance (60mm_??_70mm) for the operation of such a pump. Maximum Ho-Coefficient obtained so far is about 40%. When the inclined wall is made perpendicular to the pumping direction, however, the characteristics are worse than the former.
On the basis of these results, the mechanism and the advantages of Alexander type pump are discussed.
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