| 摘要 |
A reverse circulation valve includes a cylindrical housing having an open longitudinal passageway disposed therethrough and a circulating port and a power port disposed through a wall thereof. A valve mandrel is slidably received in the housing and movable from a closed position closing the circulating port to an open position opening the circulating port. The valve mandrel includes an annular piston received in the housing for moving the valve mandrel from its closed position to its open position. The power port communicates the piston with a pressure exterior of the housing. A frangible restraining structure is located between the valve mandrel and the cylindrical housing for restraining movement of the valve mandrel from its closed position to its open position until the pressure exterior of the housing exceeds a predetermined value, and for frangibly releasing the valve mandrel when said pressure exterior of the housing exceeds said predetermined value. The frangible restraining structure includes a carrying structure arranged for force transmitting engagement with a surface of the valve mandrel. The carrying structure includes inner and outer concentric sleeves with the inner sleeve being arranged for said force transmitting engagement with the surface of the valve mandrel. Shear pins are connected between the inner and outer concentric sleeves and arranged to be sheared upon relative longitudinal movement between the inner and outer cylindrical sleeves. |
