GB1345460A - Method and apparatus for testing the gas permeability of foils - Google Patents

Abstract

1345460 Measuring gas permeability G H LYSSY 15 Nov 1972 [18 April 1972] 52807/72 Heading G1N To measure the gas permeability of a foil a pressure differential is initially set up across the foil, then the rise of pressure on the low side due to passage of gas through the foil is measured using a Pirani heated wire gauge. In Fig. 1 a chamber 11 is defined by two parts 10, 12 clamped together, rubber seals 18, 19 ensuring a gas tight joint. The foil to be tested covers a porous sheet 17, and is shown at f. The gas to be used is admitted at pipes 14, and then chamber 13 is evacuated by pump P via valve 3. The pressure in chamber 13 slowly rises, and at a given value the output from Pirani gauge 21, 22 is recorded on recorder 5; the recording continues until a higher predetermined pressure is reached, then when the pressure reaches a yet higher value preset at control unit 4 the valve 3 is opened and chamber 13 is evacuated again so that the measurement is repeated. The pressure to which chamber 13 is evacuated is also preset at unit 4. The pressures at which recorder 5 switches on and off may be set by contact devices on its scale 51. The measurements are repeated until the length of time for which recorder 5 operates becomes constant, this being necessary because the gas permeability tends to rise after the initial measurements. To calculate the permeability in cm<SP>3</SP> per m<SP>2</SP> per 24 hours at N.T.P., the foil area and the volume of chamber 13, pipes 15, 16 and the pore volume of plate 17 must be correlated. Recorder 5 carries out this calculation and prints the result; alternatively the timing and calculation may be done manually. The recorder 5, and control unit 4 both use temperature compensated bridges to determine the Pirani gauge resistance and hence the pressure; unit 4 may be combined with the recorder, or replaced by manual operation.