A valve connector for hemodialysis lines includes a male luer lock valved fitting, a female luer lock fitting that can be engaged with the male luer lock fitting, and a rotatable ring nut carried by the male luer lock fitting and that can be screwed with the female luer lock fitting. Before the rotatable ring nut begins the screwing on the female luer lock fitting, the male luer lock valved fitting is fully opened, and as soon as the ring nut ceases the unscrewing from the female luer lock fitting, the male luer lock valved fitting fully closes instantly.