| 摘要 |
<p>A seal (38) is provided to prevent contamination by sand or grit in the clearance (28) between a flow tube (26) and the inner housing wall (16) in a safety valve. An enlarged space is provided adjacent the seal to allow accumulation of sand or grit in the annular clearance space without causing seizure of the flow tube. Disclosed is also an insert safety valve which is assembled without a spacer and with a seal mounted to the lower end of the insert valve to engage the bottom sub on the SSV. As a result, particularly for larger sizes of insert safety valves, the assembly is lighter and shorter, which facilitates use of readily available standard lubricator and wireline equipment.</p> |
