Metering device for controlling low rates of flow between regions of widely-different pressures

Claim 1

IN A GAS DRYING SYSTEM THAT COMPRISES A DESICCANTTYPE DRYER, A HIGH PRESSURE GAS RECEIVER, AND MEANS FOR DELIVERING DRY GAS FROM SAID DRYER TO SAID GAS RECEIVER; MEANS FOR RETURNING A SMALL QUANTITY OF SAID DRY GAS FROM SAID RECEIVER TO SAID DRYER TO REACTIVATE SAID DRYER, COMPRISING: (A) A GENERALLY HELICAL LONG METALLIC TUBE OF A GENERALLY HELICAL FORM DEFINING A CAPILLARY PASSAGE EXTENDING BETWEEN OPPOSITE ENDS OF SAID TUBE AND CONNECTING SAID RECEIVER TO SAID DRYER, (B) A PAIR OF FITTINGS RESPECTIVELY LOCATED AT THE OPPOSITE ENDS OF SAID TUBE, MEANS JOINING SAID FITTINGS TO SAID TUBE IN PRESSURE-TIGHT RELATIONSHIP FOR SUBSTANTIALLY PREVENTING LEAKAGE BETWEEN SAID TUBE AND SAID FITTINGS, (C) EACH OF SAID FITTINGS HAVING AN OPENING EXTENDING THERETHROUGH AND COMMUNICATING WITH SAID CAPILLARY PASSAGE, SAID OPENING HAVING A LARGER CROSS-SECTION THAN THAT OF SAID CAPILLARY PASSAGE, (D) A POROUS METAL FILTER IN THE OPENING IN EACH OF SAID FITTINGS ARRANGED IN THE PATH OF ANY GAS FLOWING THROUGH SAID CAPILLARY PASSAGE AND SPACED FROM SAID CAPILLARY PASSAGE, SAID POROUS METAL FILTER HAVING PORES MUCH SMALLER IN CROSS-SECTION THAN THE CROSSSECTION OF SAID CAPILLARY PASSAGE, (E) A TUBULAR HOUSING JOINED AT ITS RESPECTIVE OPPOSITE ENDS TO SAID FITTINGS AND SURROUNDING SAID METALLIC TUBE, (F) AND PRESSURE-RELIEVING MEANS AFFORDING FREE COMMUNICATION BETWEEN THE INTERIOR AND EXTERIOR OF SAID HOUSING.