GB1488954A - Leakage test method - Google Patents

Abstract

1488954 Leak detecting MASCHINENFABRIK AUGSBURG-NURNBERG AG 20 Jan 1975 [24 Jan 1974] 2298/75 Heading G1S A leak in a hollow body is detected by introducing the body into a leak proof test chamber, removing air from the space within the hollow body and the space within the test chamber, introducing tracer gas into one of the said spaces, removing any gas passed to the space not fed with tracer gas and comparing the amount of gas removed with the amount of tracer gas absorbed through a calibrated leak, the tracer gas from the other space being removed and collected. Hollow bodies 1 and 31 to be leak tested are placed under bell jars 4, 34 and evacuated to about 0À5 Torr together with the jars by a pump 6 by way of valves 7, 8; 37, 38. At this reduced pressure valves 7, 37 automatically close, but the bell jars are further evacuated. A valve 9 opens as soon as valves 7 and 37 close and the bodies 1, 31 are further reduced in pressure by way of valves 13, 43 and pump 15, a cooling trap of liquid nitrogen 14 absorbing oil and water vapours which might damage the control circuit. At the same time the trap 14 produces a pressure gradient to the leakage finder 16, and pressure measuring points P control a previously programmed control device which largely automatically controls and monitors the testing apparatus. A progressively opening valve 17 leading to the leakage finder 16 receives its opening impulse from a pressure switch 18 but receives its command for remaining at a particular degree of openness from the pressure measuring device in the leakage finder itself. Quantitive measurement of the leakage rate is possible if 17 is inhibited at a certain degree of opening by passing only a predetermined portion of the gas flow to the detector. A tracer gas (helium) is then passed into the bell jars from a storage container 21 via valves 19, 12, and 42 until a predetermined pressure is reached. The time for the pressure to rise and hold for measurement must be determined by preliminary tests but any tracer gas passing through into the hollow bodies is detected by 16 which gives a leakage rate which is compared with the leakage rate through a calibrated leak 29 which has previously been evacuated by a pump 26 and valve 27. After the test, or if an excessive leakage rate is already indicated during inflow of the tracer, valve 19 closes and valve 20 opens to compress the tracer gas back into 21 via pump 23 and filters 24. Following this, air is admitted into the jars through valves 11 and 41 and an inert oxidation preventing gas such as nitrogen is then admitted into the hollow bodies which are still sealed by closure devices 25, 55. The inert gas may be introduced into that space not fed with tracer gas to enable a desired safe pressure gradient to be obtained between the interiors of the hollow bodies and the interiors of the bell jars.