Sensing the open and/or closed condition of valves

摘要: A valve is disclosed which includes a first magnetic sensing means (71) and closely positioned second (73). shaft carries material (91) moved as the opened or closed. The magnetically held in one of its states when open, by presence (91). When closed influences (73) trips it into an alarm condition. also condition Thus, there back-up being acts to provide if person should maliciously attempt fool sensors placing near subsequently close valve, without causing alarm. such brought proximity will cause trip state. Sensing fitted housing for attaching this result disclosed.