A variable gas flow meter for obtaining a differential pressure across a membrane having a variable area orifice. The orifice is defined by a hinged flap which swings open in the direction of gas flow. The area of the orifice enlarges with increased flow. The flow meter retains the membrane in a central...http://www.google.es/patents/US5033312?utm_source=gb-gplus-sharePatente US5033312 - Gas flow meter housing
