Visible filter clogging indicator

Claim 1

A TEMPERATURE SENSITIVE DIFFERENTIAL PRESSURE INDICATING DEVICE COMPRISING A HOUSING HAVING A FIRST BORE THEREIN, A PLUG FOR CLOSING ONE END OF SAID FIRST BORE, SAID PLUG HAVING A SECOND BORE THEREIN, AN INDICATOR PIN SLIDABLE WITHIN SAID SECOND BORE AND MOVABLE FROM A HIDDEN FIRST POSITION TO A VISIBLE SECOND POSITION, SAID INDICATOR PIN HAVING AN ANNULAR GROOVE FORMED THEREON, A PLURALITY OF LOCKING BALLS LOCATED IN SAID GROOVE FOR RETAINING SAID INDICATOR PIN IN SAID HIDDEN FIRST POSITION, A LOCK SLEEVE LOCATED IN SAID SECOND BORE FOR CONFINING SAID LOCKING BALLS IN SAID ANNULAR GROOVE, A FIRST PISTON MEMBER OPERATIVELY CONNECTED TO SAID LOCK SLEEVE AND MOVABLE IN SAID FIRST BORE FOR MOVING SAID LOCK SLEEVE TO A POSITION WHICH WILL PERMIT THE BALLS TO MOVE RADIALLY OUT OF SAID GROOVE, SPRING MEANS FOR OPPOSING MOVEMENT OF SAID LOCK SLEEVE AND FIRST PISTON MEMBER, A SECOND FLOATING PISTON MEMBER MOVABLE IN SAID FIRST BORE, SAID FIRST AND SECOND PISTON MEMBERS FORMING A CHAMBER THEREBETWEEN WITHIN SAID FIRST BORE, STOP MEANS LOCATED IN SAID CHAMBER FOR PREVENTING CONTACT BETWEEN SAID FIRST AND SECOND PISTON MEMBERS, FLUID TEMPERATURE SENSITIVE MEANS CONFINED IN SAID CHAMBER FOR TRANSMITTING MOTION FROM ONE OF SAID PISTON MEMBERS TO THE OTHER, SAID STOP MEANS PREVENTING TRANSMITTAL OF SUCH MOTION AT TEMPERATURES CAUSING SAID FLUID MEANS TO SOLIDIFY, A FIRST PORT FOR COMMUNICATING ONE SIDE OF SAID FIRST PISTON MEMBER AND ONE END OF SAID INDICATOR PIN WITH A FIRST PRESSURE, AND A SECOND PORT FOR COMMUNICATING ONE SIDE OF SAID SECOND PISTON MEMBER WITH A SECOND PRESSURE.