| 摘要 |
The apparatus includes a main vacuum source (PA) that can be connected to a series of evaporation beds (1, 1', 1") to product a negative pressure having a preset value in the beds, in steady-state operati ng conditions. There is a secondary vacuum source (P B) which is suitable to produce, in one bed at a time, a negative pressure which is close to the steady-state value, and there is a valve means to selectively connect each bed, which is initially at ambient pressure, first to the secondary vacuum source (P B) and then to the main vacuum source (P A), so as to eliminate substantial pressure variations in the remaining beds when each bed is connected to the main vacuum source. The valve means includes, for each bed, a first electric valve (4, 4', 4") o n a line for connection to the outside environment, a second electric valve (5, 5', 5") on a line (3, 3', 3") for connection to the secondary vacuum source (P B), and a third electric valve (6, 6', 6") on a line (2, 2', 2") for connection to the main vacuum source (P A). There is also a control unit (7) suitable to control the cyclic sequential opening and closure of the first, second and third electric valves of each bed.
|
