Inhalation valve

An inhalation valve comprising a cylindrical body of predetermined diameter to provide bidirectional flow therethrough and having an open first end and an open second end, a cylindrical mouthpiece joined to said body at said second end and forming a straight-through continuation of said body, a flow tube substantially smaller diameter than said predetermined diameter disposed within said body adjacent to and connected to one side thereof and oriented axially thereof and open at both ends providing an inhalation flow path through said body, partition means disposed substantially diametrically of said body and extending substantially from said first end substantially to said second end and demarcating a portion of said body exteriorly of said tube as an exhalation flow path, a single substantially circular flexible diaphragm, means mounting said diaphragm substantially diametrically thereof at the second end of said body with first and second portions of said diaphragm respectively lying across said inhalation and said exhalation flow paths, a transverse wall covering substantially half of said second end of said body and through which said flow tube opens, said wall being upstream of said diaphragm and forming a back-up for the second portion of said diaphragm to prevent exhalation through said flow tube and permitting flexing of said second portion of the diaphragm to permit inhalation through said flow tube, back-up means downstream of said diaphragm for the first portion of said diaphragm permitting flexing of said diaphragm first portion upon exhalation and backing up said diaphragm first portion upon inhalation to permit exhalation but prevent inhalation through said exhalation flow path, and means extending laterally through said flow tube and said body providing a lateral opening from said flow tube to permit detecting a lateral pressure drop upon inhalation.