| 摘要 |
A filter 210 including a body 214 having a plurality of apertures 220 through which fluid is able to pass wherein at least apportion of the apertures being provided in a substantially helical formation along at least a part of the length of the body. The filter may include a plurality of rows of apertures. The filter may be a mud filter for an oil well drilling string. The filter may include a fluid displacer. The at least one helical formation provided on the body of the filter may correspond with a helical formation of a or each channel of a fluid displacer. A fluid displacer for a filter, the fluid displacer includes at least one channel along which fluid is capable of passing. The channel may be provided in a helical formation. A set of channels may be provided which are connectable to a filter body and a second set of channels may be provided on a fluid transfer member. A filter sub 240 of an oil drilling string, wherein the filter sub includes a tubular body and at least one helical formation on an internal surface of the tubular body. |
