An air admittance valve (20,50) configured when subjected to a negative pressure condition to vent a pipe system to an ambient environment, said air admittance valve comprising: a main body having top and bottom portions and configured to sealingly attach to the pipe system proximate the bottom portion, the main body also defining a first chamber configured to communicate with the pipe system; - inner and outer valve seats that define at least one vent opening located between the inner and outer valve seats (95,100) and configured to communicate with the ambient environment; - a flexible sealing element configured to move between a closed position and an open position, the sealing element defining an outer perimeter surface, an inner perimeter surface, and opposite top and bottom surfaces extending between the outer and inner perimeter surfaces; - a lid configured to sealingly attach to the main body, wherein the lid further comprises one or more guiding elements that define one or more guiding surfaces configured to engage the inner perimeter surface of the sealing element so as to guide the sealing element to and from the closed position, in which the bottom surface of the sealing element rests against the inner and outer valve seats thus blocking communication through the vent opening, and the open position, in which the sealing element rises off of the inner and outer valve seats (95,100) such that the first chamber communicates with the ambient environment through the vent opening, and - a rigidifying element for the sealing element, whereby the top surface of the sealing element includes an inner support rib and an outer support rib as rigidifying element of the sealing element, said inner and outer support ribs (75,79) forming with the sealing element an unitary element devoid of rigid frame structure, and wherein the inner and outer support ribs are configured to provide support for the sealing element proximate the inner and outer valve seats (95,100), respectively. a main body having top and bottom portions and configured to sealingly attach to the pipe system proximate the bottom portion, the main body also defining a first chamber configured to communicate with the pipe system; - inner and outer valve seats that define at least one vent opening located between the inner and outer valve seats (95,100) and configured to communicate with the ambient environment; - a flexible sealing element configured to move between a closed position and an open position, the sealing element defining an outer perimeter surface, an inner perimeter surface, and opposite top and bottom surfaces extending between the outer and inner perimeter surfaces; - a lid configured to sealingly attach to the main body, wherein the lid further comprises one or more guiding elements that define one or more guiding surfaces configured to engage the inner perimeter surface of the sealing element so as to guide the sealing element to and from the closed position, in which the bottom surface of the sealing element rests against the inner and outer valve seats thus blocking communication through the vent opening, and the open position, in which the sealing element rises off of the inner and outer valve seats (95,100) such that the first chamber communicates with the ambient environment through the vent opening, and - a rigidifying element for the sealing element,