1. Field Of The Invention
The present invention relates generally to back pressure valves, and more particularly, but not by way of limitation, to back pressure valves suitable for use in a workover string for acidizing of wells.
2. Description Of The Prior Art
During certain workover jobs on oil and gas wells, a tool known as a back pressure valve is run in the work string. The back pressure valve typically is a flapper type valve which when in a closed position prevents upward flow through the work string. The flapper is opened by a stinger tube which is pushed downward through the flapper. The operation of the stinger tube is typically controlled by a J-slot interconnection between the stinger tube and the housing which contains the flapper valve. Thus, the flapper valve is opened by the weight of the workover string above the back pressure valve which is available to be set down on the stinger tube to force the flapper open. Sometimes a difficulty is encountered when there are very high pressures contained in the workover string below the flapper. The back pressure valve is typically placed at a relatively high point in the work string near the surface, and thus the weight of the work string thereabove is sometimes inadequate to force the flapper open against the high internal pressures trapped below the flapper.
Thus, there is a need for a back pressure valve which can be operated reliably regardless of the pressures acting against the flapper and holding it closed.