| 摘要 |
A pressure operated downhole tool, eg circulation valve, has an operating element (60) and operating means, eg power mandrels (42,46). When a first predetermined pressure difference is established between the annulus and the interior of the tool, the operating means will operate the operating element but only if a safety device (44) has first been actuated. The safety device is actuated by a second predetermined pressure difference in an opposite direction to the first pressure difference. In one arrangement, the tool comprises a housing (31); a circulating valve (40) comprising a circulation port (62) formed through a wall of said housing and a valve mandrel (60) slidably received in said housing for blocking said circulating port in a first position and exposing said circulating port in a second position for permitting a flow between the interior and exterior of said housing, said valve mandrel being releasably maintained in said first position; valve piston means (90) slidably received in said housing for moving said valve mandrel to said second position in response to an internal pressure increase applied from within said housing; and a safety mandrel (96) slidably received in said housing; said safety mandrel having a first position in which said valve piston means is prevented from moving said valve mandrel to said second valve mandrel position and a second position in which such movement is permitted, said safety mandrel being moved from said first safety mandrel position to said second safety mandrel position responsive to an increase in pressure exterior of said housing. |
