| 摘要 |
Wet jigging machines for treating minerals, esp. coal, employ rotary butterfly valves actuated by rotary magnets. In an initial starting up period of valve rotation, lasting e.g. 70-200 (140) milliseconds, the valve drive is supplied with high potential (50-150 volts), while during the remainder of a cycle a lesser potential (10-30 volts) is supplied. Valve rotation may be through 20-70 (50) deg. and limited by a mechanical and/or electrical stop. The two different voltages, normally DC, may be derived from separate tappings of a single transformer. Power from main supply is electrically controlled to provide the different potentials.
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