Abstract: Downhole apparatus in the form of a valve (140) comprises a body (148) defining a bore (168) with a curved disc closure member (142) positioned in the bore. First and second retaining members (144, 146) are positioned on respective sides of the disc (142) for retaining the disc in a closed position and to hold pressure from both sides. One of the retaining members (144) is retractable to permit opening of the valve disc (142). The disc (142) may be locked closed by locking the retractable retaining member (144) in position. On release of the member (144), application of fluid pressure to portions of the member (144) will retract the member (144).

Abstract: A method of locating a tubing string in a bore, the method comprising the steps: providing a device defining a restriction-engaging member; locating the device on the lower end of a tubing string; and then running the tubing string into the bore until the member engages a restriction in the bore and the device and the tubing is prevented from advancing further by the restriction. The member is then re-configured to permit further advancement of the device and tubing relative to the restriction and the device and tubing moved a predetermined distance relative to the restriction to position the tubing at a desired location in the bore.

Abstract: Downhole apparatus in the form of a valve (140) comprises a body (148) defining a bore (168) with a curved disc closure member (142) positioned in the bore. First and second retaining members (144, 146) are positioned on respective sides of the disc (142) for retaining the disc in a closed position and to hold pressure from both sides. One of the retaining members (144) is retractable to permit opening of the valve disc (142). The disc (142) may be locked closed by locking the retractable retaining member (144) in position, On release of the member (144), application of fluid pressure to portions of the member (144) will retract the member (144).

Abstract: Downhole apparatus in the form of a valve (140) comprises a body (148) defining a bore (168) with a curved disc closure member (142) positioned in the bore. First and second retaining members (144, 146) are positioned on respective sides of the disc (142) for retaining the disc in a closed position and to hold pressure from both sides. One of the retaining members (144) is retractable to permit opening of the valve disc (142). The disc (142) may be locked closed by locking the retractable retaining member (144) in position. On release of the member (144), application of fluid pressure to portions of the member (144) will retract the member (144).