Pinch element plastic valve

A valve has a contractible valve element formed of an inner laminae of PFA, an outer laminae of PTFE with the outer laminae having a boss to provide positive compression and positive distension of the valve element. The portion that constrict is welded to a PFA tubular end portion thus providing the advantages of a PTFE laminae with a boss and the PFA what it surfaces. The valve utilizes a valve mechanism which has a yoke which moves radially towards and away from the contractible valve element with linkages extending from yoke arms which connect to opposite sides of the contractible valve element. The valve element may thus be positively closed and positively opened. The hermetic seal between the outer PTFE laminae and the inner PFA laminae causes the inner laminae to extend outwardly when the outer laminae is positively distended thereby allowing the valve function where the fluid being controlled is under a negative pressure. The invention also includes the method of manufacturing the multiple layered valve element.