A high conductance valve for use in fluid delivery systems is comprised of a flat non-circular orifice ridge adjacent to which a control plate having a planar control surface is proximally positioned to adjust the valve effective opening area and thereby the conductance of the valve. The length of the non-circular orifice ridge periphery is substantially greater than the circumference of a similarly sized circular orifice and therefore the realized effective opening area is also substantially greater despite having a similar footprint.