| 摘要 |
Pressure operated circulation valve with releasable safety and method for operating the same. A valve mandrel slidably received within a housing is frangibly restrained in a lower position blocking a circulation port through the housing. An upper power mandrel is frangibly restrained in a lower position beneath the valve mandrel for moving the valve mandrel upwardly responsive to an increase in internal housing pressure. A safety mandrel is frangibly restrained beneath the upper power mandrel and blocks communication of internal housing pressure to the lower end of the upper power mandrel until the safety mandrel is moved upwardly responsive to an increase in annulus pressure. Thus, the circulation valve is opened by first raising the annulus pressure by a pre-determined amount and thereafter increasing internal housing pressure.
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