A leakage data point represented a mean value of five measurements. fiber insertion and arch dent on the valve seat, were used to investigate the effect of leak shape on the characteristic leak flow as a function of pressure drop. Seven valves of each brand were tested for leakage rate at pressure drops ranging from 15 to 45 mmH 2O (or extended to 75 mmH 2O for some valves). To study the characteristics of leakage through exhalation valves, a leakage meter was built to measure the leakage rate of four brands of exhalation valves. However, the test alone might not reflect the leakage rate under different levels of vacuum. Certification tests currently employed by some industrialized nations to certify respirators require that when challenged with air flow at a constant suction head of 25 mmH 2O, the leakage into the facepiece from the exhalation valve(s) should not exceed 30 ml min −1.
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