of the air pulse the coarse particles then fall to the coarse outlet 22 by gravity after the compressed air valve is closed air and particle flow is again caused to flow through inlet 19 and the unclogged screens allow additional fines to pass through generally the jet pulse of air through each venturi should take place for about 0 1 seconds for each compressed air valve in sequence the total sequence time will ordinarily range from 30 seconds to several minutes depending on the tendency of the coarse particles in the material being screened to build up the downward tilt of the housing and tubesheet promotes the flow of coarse material towards the coarse outlet from both the topside of the screens and the tubesheet the acute angle of tilt is shown as approximately 45 u00b0 from the horizontal although the angle may vary in magnitude depending on the flow properties of the material in a number of operations the housing and tubesheet may be aligned horizontally the present device also offers the advantage of increased active screen area over flat screens used as separators a normal flat screen occupying a floor area of 6 39 u00d7 6 39 would have a screen area of about 36 sq ft the present device can be contained in the same 6 39 u00d7 6 39 floor area having 49 screen elements each having approximately 4 sq ft of screen area this would provide a total of 196 sq ft of screen area over 5 times the active screen area of the flat screen fig1 also shows an alternate embodiment.