| 摘要 |
A check valve for use downhole in the production tubing of an oil and gas well. The check valve comprises a tubular valve body including a valve seat plate having an upper surface, a lower surface, an upflow orifice and a downfloworifice, a first valve ball contained within a ball cage which may seat on the upper surface of the valve seat plate closing the upflow orifice, a second valve ball contained within a downflow valve housing which may seat on the lower surface ofthe valve seat plate to close the downflow orifice. The second valve ball is biased in the closed position by a coil spring mounted within the downflow valve housing. Fluid pressure from below the check valve unseats the first valve ball allowing upward flow of fluid through the check valve and the production tubing. Fluid pressure from above the check valve will cause the first valve ball to seat and close while the second ball remains seated due to the coil spring. In that position, no downward flow of fluid is allowed. Additional pressure may be intentionally applied to partially compress the coil spring and unseat the second valve ball, allowing downward flow of fluid through the check valve and thus the production tubing. At even greater pressure, the coil spring is completely compressed, allowing the second valve ball to seat on a second valve seat opposite the valve seat plate. Again, no downward flow of fluid is permitted in this position.
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