A vent subassembly includes a vent body having an opening which is covered or uncovered dependent upon the location of a vent sleeve relative to the vent body. The vent subassembly can be connected below a packer, and the vent sleeve can be connected to a perforator so that movement of the vent sleeve...http://www.google.fr/patents/US4800958?utm_source=gb-gplus-shareBrevet US4800958 - Annulus pressure operated vent assembly
