| 摘要 |
A filter element has a first flow path adapted to restrict the passage of particles there through and a second flow path that is constantly open. Preferably, the filter element has multiple small openings 36 and at least one large opening 38 so that, when none of the openings are plugged, the probability of solid particles carried by a flow of fluid becoming trapped in the region of the first openings is higher than that of the particles passing through the second openings. The filter, in tubular form 40, can be used in a drill string to remove particles from drilling mud that operates a downhole tool 18 such as a stabiliser. Should the small perforations become blocked, mud can still reach the stabiliser via the bypass openings. The filter works with flow either radially outwards or radially inwards through the filter element. |
