Tank drain valve with a rod concentric with valve member to pierce sedimentary layer in tank

A valve comprising a body adapted to be associated with an opening in the wall of a fluid reservoir or flowline, to provide a flow path, from an inlet at said opening, to an outlet, a valve seat located across the flow path at the inlet, a valve member movably supported from the body to be movable between a closed position at which it is in sealing engagement with the valve seat and an open position at which it is spaced from the valve seat, an elongate clearing element for clearing scale or sediment in the region of the opening, the clearing element being slidably supported within the valve member for axial movement within the valve member, the clearing element having an outer end which is movable towards and away from the valve member between an extended position at which it extends from the valve member through the valve seat beyond the opening and a retracted position closely adjacent the valve member, the valve member further including a first drive means, which includes at least one of a seal and a piston, being received in a cylindrical first chamber which is concentric to the valve member, the first drive means defining two spaces within the chamber and the spaces being capable of receiving pressurized fluid for acting on the drive means to effect said movement of the valve member, the elongate clearing element including a second drive means that includes at least one of a piston and a seal, and wherein the valve includes at least a third space for receiving pressurized fluid for acting on the second drive means for effecting said axial movement of the clearing element.