| 摘要 |
The invention is a differential fill valve apparatus principally for use in treating earth wells, usually in connection with cementing a string of casing into the well bore. The apparatus, at or near the low end of the casing, has a pressure actuated slidable piston which rises as liquid is encountered in the well bore opening parts for admitting liquid into the casing until the pressure from liquid in the casing reaches a predetermined ratio with respect to the pressure in the well bore annulus.
|
