Pilot operated pressure and vacuum relief valve

Claim 1

IN A RELIEF VALVE OF THE TYPE HAVING A BODY AND NORMALLY CLOSED POPPET MECHANISM HAVING A FRONT PORTION WHICH IS ADAPTED TO BLOCK TRANSFER OF PRESSURE FLUID BETWEEN A HIGH PRESSURE FLUID SUPPLY LINE AND A LOW PRESSURE FLUID RETURN LINE IN SAID NORMALLY CLOSED POSITION THEREOF, AND WHEREIN PRESSURE FLUID SUPPLY LINE PRESSURE IS NORMALLY MAINTAINED IN A CHAMBER IN THE BODY, INTO WHICH THE POPPET MECHANISM PROJECTS, SO THAT SUCH PRESSURE FLUID NORMALLY EXERTS FORCE ON A REAR PORTION OF THE POPPET MECHANISM TO HOLD THE SAME IN SAID CLOSED POSITION THEREOF, SAID RELIEF VALVE BEING CHARACTERIZED BY: (A) MEANS DEFINING A PAIR OF PASSAGES CONNECTING WITH SAID CHAMBER AND THROUGH EITHER OF WHICH FLUID IN THE CHAMBER MAY BE SUBSTANTIALLY FREELY EXHAUSTED TO ALLOW THE POPPET MECHANISM TO BE OPENED UNDER FLUID PRESSURE FORCES EXERTED UPON ITS FRONT PORTION, ONE OF SAID PASSAGES PROVIDING A CONTROL PASSAGE THAT IS COMMUNICABLE WITH THE FLUID SUPPLY LINE AND THROUGH WHICH SUPPLY LINE FLUID NORMALLY FLOWS INTO SAID CHAMBER; (B) A PILOT POPPET IN THE BODY BIASED TO A CLOSED POSITION BLOCKING THE OTHER OF SAID PASSAGES BUT MOVABLE TO A CHAMBER EXHAUSTING POSITION IN CONSEQUENCE OF THE FORCE WHICH SUPPLY LINE FLUID EXERTS THEREON AT TIMES WHEN ITS PRESSURE RISES TO A PREDETERMINED RELIEF VALUE; (C) AND MEANS PROVIDING A THROTTLING VALVE FOR SAID CONTROL PASSAGE, THAT IS INEFFECTIVE AS LONG AS THE PILOT POPPET IS CLOSED, BUT IS RENDERED OPERATIVE TO SUBSTANTIALLY RESTRICT THE CONTROL PASSAGE IN RESPONSE TO THE DROP IN PRESSURE THAT TAKES PLACE IN THE CHAMBER AT TIMES WHEN THE PILOT POPPET OPENS.