end 14 with pin type threading 16 for attachment to an adjacent section of production tubing not shown and a second axial end 18 with box type threading 20 for attachment to an adjacent section of tubing not shown the valve housing 12 defines an axial flowbore 22 along its length having an enlarged central section 24 an annular valve seat 26 is secured within the enlarged central section 24 in this instance it is desired to block fluid flowing from the second end 18 toward the first end 14 therefore the second end 18 will be considered to be upstream from the first end 14 a flapper valve member 28 is hingedly secured to the valve seat 26 by hinge pin 30 the valve member 28 is rotationally moveable about the hinge pin 30 between an open position shown in fig2 and a closed position fig1 wherein the valve member 28 contacts and is seated upon the valve seat 26 a torsion spring not shown biases the valve member 28 toward its closed position when in the closed position depicted in fig1 the valve assembly 10 blocks fluid flowing downstream from the second end 18 toward the first end 14 of the housing an equalizing port assembly the structure and function of which will be described shortly is generally indicated at 32 an axially shiftable actuation member which may be a conventional actuation tube or sleeve 34.