Visible filter clogging indicator

Claim 1

A TEMPERATURE SENSITIVE DIFFERENTIAL PRESSURE INDICATING DEVICE COMPRISING A HOUSING HAVING A BORE THEREIN, A CAGE LOCATED IN ONE END OF SAID BORE, SAID CAGE HAVING A PLURALITY OF AXIAL SLOTS FORMED THEREIN AND NOTCHES FORMED ON THE END THEREOF, A HOLLOW INDICATOR BUTTON SLIDABLE WITHIN SAID CAGE AND MOVABLE FROM A HIDDEN FIRST POSITION TO A VISIBLE SECOND POSITION, SAID INDICATOR BUTTON HAVING HELICAL SLOTS FORMED IN THE WALLS THEREOF AND PROJECTIONS EXTENDING THEREFROM, SAID PROJECTIONS BEING LOCATED IN SAID AXIAL SLOTS OF SAID CAGE FOR PREVENTING RELATIVE ROTATION BETWEEN SAID INDICATOR BUTTON AND SAID CAGE, A SPRING FOR URGING SAID INDICATOR BUTTON FROM SAID HIDDEN FIRST POSITION TO SAID VISIBLE SECOND POSITION, A SHAFT LOCATED WITHIN SAID INDICATOR BUTTON AND EXTENDING SUBSTANTIALLY THE LENGTH OF SAID CAGE, SAID SHAFT HAVING A TRANSVERSE SLOT FORMED ON ONE END THEREOF AND A TRANSVERSE PIN EXTENDING THROUGH THE OTHER END THEREOF FOR ENGAGEMENT WITH THE HELICAL SLOTS IN SAID INDICATOR BUTTON, SAID TRANSVERSE PIN THEREBY PREVENTING MOVEMENT OF SAID INDICATOR BUTTON TO A VISIBLE POSITION EXCEPT WHEN SAID SHAFT IS PERMITTED TO ROTATE WITH RESPECT TO SAID INDICATOR BUTTON AND CAGE, A LOCKING PIN LOCATED IN THE TRANSVERSE SLOT OF SAID SHAFT AND THE NOTCHES OF SAID CAGE FOR PREVENTING RELATIVE ROTATION BETWEEN SAID SHAFT AND SAID CAGE, A PISTON MEMBER OPERATIVELY CONNECTED TO SAID LOCKING PIN AND MOVABLE IN SAID BORE FOR PERMITTING EGRESS AND INGRESS OF SAID LOCKING PIN FROM THE NOTCHES OF SAID CAGE, A FLEXIBLE BLADDER LOCATED IN SAID BORE, SAID PISTON MEMBER AND BLADDER FORMING A CHAMBER THEREBETWEEN WITHIN SAID BORE, SPRING MEANS LOCATED IN SAID CHAMBER FOR OPPOSING MOVEMENT OF SAID PISTON MEMBER AND SECURING THE END OF SAID BLADDER TO SAID HOUSING, FLUID TEMPERATURE SENSITIVE MEANS CONFINED IN SAID CHAMBER FOR TRANSMITTING FORCES FROM THE BLADDER TO THE PISTON MEMBER, SAID FLUID MEANS SOLIDIFYING AT TEMPERATURES BELOW A PREDETERMINED VALUE TO THEREBY PREVENT MOVEMENT OF SAID PISTON, A FIRST PORT FOR COMMUNICATING ONE SIDE OF SAID PISTON MEMBER WITH A FIRST PRESSURE, AND A SECOND PORT FOR COMMUNICATING ONE SIDE OF SAID BLADDER WITH A SECOND PRESSURE.