A valve comprises a first housing including a first lumen extending therethrough and defining a first disk-facing surface and a second housing including a second lumen extending therethrough and defining a second disk-facing surface, the second housing being mated to the first housing so that the second disk-facing surface faces the first disk-facing surface in combination with a flexible disk gripped between gripping portions of the first and second disk-facing surfaces, the disk including a slit extending therethrough which, when acted upon by a fluid pressure of at least a predetermined threshold level opens to permit fluid flow between the first and second lumens and which, when acted upon by a fluid pressure less than the threshold level remains sealed preventing fluid flow between the first and second lumens and a relief well between opposing portions of the first and second housings radially outside the gripping portions, a width of the relief well exceeding a width of a radially outer portion of the flexible disk so that the radially outer portion of the disk is free to move therewithin.