Differential pressure indicator and switch

Claim 1

A PRESSURE SWITCH COMPRISING (A) PRESSURE SENSITIVE MEANS ADAPTED TO MOVE WITH CHANGE IN PRESSURE; (B) A LIGHT INTERRUPTING MEMBER; (C) A LIGHT SOURCE ON ONE SIDE OF SAID LIGHT INTERRUPTING MEMBER; (D) A PHOTOSENSITIVE DEVICE ON THE OTHER SIDE OF SAID LIGHT INTERRUPTING MEMBER, SAID DEVICE CONDUCTING CURRENT WHEN EXPOSED TO THE LIGHT SOURCE AND BEING A NON-CONDUCTOR WHEN NOT EXPOSED TO THE LIGHT SOURCE; (E) A ROTATABLY MOUNTED MAGNETIZED HELICAL CORE; (F) A MAGNETIC ARMATURE OPERATIVELY MOUNTED WITH RELATION TO SAID CORE, SAID ARMATURE BEING MOUNTED AT THE FREE END OF A CANTILEVER SPRING WHICH IS RIGIDLY MOUNTED AT ITS OTHER END; (G) SAID SPRING BEING OPERATIVELY CONNECTED TO SAID PRESSURE SENSITIVE MEANS IN SUCH MANNER AS TO CAUSE THE FREE END THEREOF AND THE ARMATURE MOUNTED THEREON TO MOVE IN UNISON WITH SAID PRESSURE SENSITIVE MEANS; (H) SAID INTERRUPTING MEMBER BEING MOUNTED TO ROTATE IN UNISON WITH SAID HELICAL CORE AND BEING SIZED AND POSITIONED SO AS TO MOVE INTO AND OUT OF THE STRAIGHT LINE PATH BETWEEN SAID LIGHT SOURCE AND PHOTOSENSITIVE DEVICE UPON PREDETERMINED POSITIONS OF SAID ARMATURE; (I) MEANS FOR CONNECTING SAID LIGHT SOURCE TO A SOURCE OF ELECTRIC POTENTIAL; (J) MEANS FOR CONNECTING SAID PHOTOSENSITIVE DEVICE TO A SOURCE OF ELECTRIC POTENTIAL; AND (K) MEANS FOR CONNECTING SAID PHOTOSENSITIVE DEVICE IN SERIES WITH A RELAY.