The pump body with a diameter of D < 250mm is made of seamless steel pipe, and the pump body of the large pump is welded by coiling a cylinder of steel plate 4 ~ 10mm thick, and the weld seam can not leak. The inner wall of the pump should be polished and nickel plated.
The pump body of the convex cavity can increase the pumping speed without increasing the size of the pump port. The convex cavity pump body changes the straight cylinder pump body into a local drum shaped convex cavity pump body. The processing method is still welded by steel plates. The bottom section of the pump is the same as the inlet diameter of the pump flange, but the pump body enlarges the pump chamber at the lower part of the inlet flange, and the enlarged diameter extends to the pump wall where the second-stage nozzle jets directly. Because of the convex cavity of the pump body, the pumping space is enlarged, the conductivity between the first and second stage nozzles is increased, and the pumping speed is also increased.
Ultra high vacuum pump oil is also a very important problem. The improper surface temperature of the pump wall makes it difficult for the oil vapor molecules colliding on the inner surface of the diffusion pump to coagulate. The surface temperature of the oil layer flowing down the pump wall is higher than that of the pump wall, so it is easy to produce re-evaporation and form oil vapor reflux. Therefore, the cooling efficiency of the pump wall is high. Generally, the pump wall is welded with spiral copper pipe or made into a water jacket form (also can be fitted with spiral steel wire in the middle of the water jacket). The cooling part of the pump is usually confined to the area where the steam flow can be ejected, so that the oil condensed from the top receives a higher degree of heat before returning to the oil pan, so that the dissolved gas in the oil is released, so as to prevent it from mixing with the oil vapor into the nozzles at all levels, affecting the vacuum of the pump.
| Dry vacuum pump |
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