A needleless access connector for connecting medical devices, the connector comprising: a housing comprising a male Luer fitting at one end; and a female Luer fitting at the other end; and a collapsible valve (200, 304) disposed in a cavity of the housing, the collapsible valve having a first axial length from 15.75 to 20.83 mm and comprising: a cylindrical first portion (200A, 304A) with at least one arcuate cut (200D, 304B) in a section thereof and having a second axial length, wherein the first portion (200A, 304A) of the collapsible valve (200, 304) creates a seal at an opening of the housing; and a cylindrical second portion (200B, 304C) being coupled to the first portion (200A, 304A) and having a void, a third axial length, and an annular outside surface over the entire third axial length, wherein the annular outside surface spans 56% of the first axial length of the collapsible valve, wherein the collapsible valve (200, 304) is configured to provide a positive displacement when collapsed by insertion of a male luer into the opening such that a fluid is allowed to move around the valve (200, 304) and between the male and female Luer fittings, and wherein the housing and collapsible valve are configured to provide and a priming volume that is from 0.17 to 0.19 milliliters. a housing comprising a male Luer fitting at one end; and a female Luer fitting at the other end; and a male Luer fitting at one end; and a female Luer fitting at the other end; and a collapsible valve (200, 304) disposed in a cavity of the housing, the collapsible valve having a first axial length from 15.75 to 20.83 mm and comprising: a cylindrical first portion (200A, 304A) with at least one arcuate cut (200D, 304B) in a section thereof and having a second axial length, wherein the first portion (200A, 304A) of the collapsible valve (200, 304) creates a seal at an opening of the housing; and a cylindrical second portion (200B, 304C) being coupled to the first portion (200A, 304A) and having a void, a third axial length, and an annular outside surface over the entire third axial length, wherein the annular outside surface spans 56% of the first axial length of the collapsible valve, wherein the collapsible valve (200, 304) is configured to provide a positive displacement when collapsed by insertion of a male luer into the opening such that a fluid is allowed to move around the valve (200, 304) and between the male and female Luer fittings, and wherein the housing and collapsible valve are configured to provide and a priming volume that is from 0.17 to 0.19 milliliters. a cylindrical first portion (200A, 304A) with at least one arcuate cut (200D, 304B) in a section thereof and having a second axial length, wherein the first portion (200A, 304A) of the collapsible valve (200, 304) creates a seal at an opening of the housing; and a cylindrical second portion (200B, 304C) being coupled to the first portion (200A, 304A) and having a void, a third axial length, and an annular outside surface over the entire third axial length, wherein the annular outside surface spans 56% of the first axial length of the collapsible valve, wherein the collapsible valve (200, 304) is configured to provide a positive displacement when collapsed by insertion of a male luer into the opening such that a fluid is allowed to move around the valve (200, 304) and between the male and female Luer fittings, and wherein the housing and collapsible valve are configured to provide and a priming volume that is from 0.17 to 0.19 milliliters.