A surgical access assembly for use with a surgical access device, which comprises: a housing defining a central longitudinal axis; an elongate access member extending from the housing, the housing and the access member having a longitudinal passage dimensioned to permit passage of a surgical instrument; an instrument seal disposed within the housing and being adapted to establish a substantial fluid tight seal about the instrument; and a zero closure valve mounted relative to the housing and being adapted to assume an open condition upon passage of the surgical instrument and a substantially closed position in the absence of the instrument, the zero closure valve including a valve periphery and first and second lips depending from the valve periphery, the first and second lips having lip edge surfaces in juxtaposed relation to define a slit when the valve is in the closed position thereof, the lips having a general arcuate internal lip surface leading to the lip edge surface to define a sloping configuration dimensioned to facilitate passage of the surgical instrument through the valve, the internal arcuate lip surface of each of the first and second lips includes an outer surface portion arranged at a first angle "k" relative to the longitudinal axis of the housing and an inner surface portion arranged at a second angle "m" relative to longitudinal axis and different from the first angle "k" characterized by: each of the first and second lips includes a support rib depending from the inner surface portion, the support ribs defining a gap therebetween to be in spaced relation when the valve is in the closed position and being positioned to contact the surgical instrument during insertion through the first and second lips. a housing defining a central longitudinal axis; an elongate access member extending from the housing, the housing and the access member having a longitudinal passage dimensioned to permit passage of a surgical instrument; an instrument seal disposed within the housing and being adapted to establish a substantial fluid tight seal about the instrument; and a zero closure valve mounted relative to the housing and being adapted to assume an open condition upon passage of the surgical instrument and a substantially closed position in the absence of the instrument, the zero closure valve including a valve periphery and first and second lips depending from the valve periphery, the first and second lips having lip edge surfaces in juxtaposed relation to define a slit when the valve is in the closed position thereof, the lips having a general arcuate internal lip surface leading to the lip edge surface to define a sloping configuration dimensioned to facilitate passage of the surgical instrument through the valve, the internal arcuate lip surface of each of the first and second lips includes an outer surface portion arranged at a first angle "k" relative to the longitudinal axis of the housing and an inner surface portion arranged at a second angle "m" relative to longitudinal axis and different from the first angle "k" characterized by: each of the first and second lips includes a support rib depending from the inner surface portion, the support ribs defining a gap therebetween to be in spaced relation when the valve is in the closed position and being positioned to contact the surgical instrument during insertion through the first and second lips. each of the first and second lips includes a support rib depending from the inner surface portion, the support ribs defining a gap therebetween to be in spaced relation when the valve is in the closed position and being positioned to contact the surgical instrument during insertion through the first and second lips.