A cap, mounted upon the stem of a suction cup, is axially repositionable by axial and/or tilting movement relative to the stem to selectively close or open fluid communication between the concave space defined by the cup element of the suction cup and the ambient environment....http://www.google.es/patents/US5511752?utm_source=gb-gplus-sharePatente US5511752 - Suction cup with valve
