A valve and trigger cyclically connect a vacuum and a blower to a filter. The valve box has three openings, the first connectable to the vacuum, the second connectable to the blower and the third connectable to the filter. A gate inside the box, biased by the blower and the vacuum toward closing the first opening, is held against the bias by a trigger outside the box to close the second opening. The external trigger intervally operates to release the interior gate to close the first opening and open the second opening. The blower operates only if the trigger is operating. The gate is released once for approximately 1/12 of a cycle interval during each trigger operating interval. A plurality of valves can be combined in a system with one trigger for cyclically sequentially connecting a plurality of filters to the vacuum and the blower.