Development and Application of a Dynamic Leakage Test Method for Exhalation Valves

1. Valve only Clean air Clean air Exhalation valve Aerosol generator Neutralizer Dryer Valve+cover Breathing simulator X Sampling tube DP Valve+cover+foam Exhaust pad = Ball valve Cin: inside concentration Cout: outside concentration Exhalation Valve For example   DP Breathing simulator Aerosol spectrometer or counter Exhaust Fig 9. Comparisons between Laerosol and Lstatic based on breathing flow rates. Fig 7. Dynamic leakage (pad) of four valves as a function of Pinhale, max. Fig 5. Calculation method and example of dynamic leakage (pad). Fig.1 Schematic of the static leakage test meter. Fig.3 Static leakage rates (Qs) of four valves as a function of pressure drop. Fig. 8 Leakage rates of Laerosol and Lstatic under different breathing conditions. Fig 4. Flow rate fluctuations of different modle CPCs under pressure variation. Fig.2 Schematic of the dynamic leakage test system. Fig.6 The effects resulting from distance (X) on pad as a function of Pinhale, max. Fig 10. The static and dynamic leakage as a function of combinations of valve cover. Development and Application of a Dynamic Leakage Test Method for Exhalation Valves Yang, C.M.; Huang, S.H.; Chen, C.C. 1Institute of Occupational Medicine and Industrial Hygiene, College of Public Health, National Taiwan University, 17, Shiu-jou Road, Taipei, Taiwan 100 Introduction There are three routes of leakage into respirator cavity, namely filter leakage, facial seal leakage and exhalation valve leakage. In general, exhalation valve is the least. As the resistance of filter increases, it will force the leakage distribution to rearrange. Therefore, when a higher protection respirator is required, the exhalation valve leakage will become more important. Certification test (static test) currently employed by USA and Australia requires that leakage into new exhalation valves should not exceed 30 mL/min at a constant suction head of 25 mmH2O, but some studies indicated the static test method cannot reflect the leakage during practical conditions. The main objectives of the research are to study the relationships between static and dynamic leakage, and explore the merits of dynamic leakage test method. Materials and Methods Four valves with static leakage rates ranging from 2 to 34 mL/min at 25 mmH2O were chosen to investigate the relationships between static and dynamic leakage, as shown in Fig.3. A static leakage test meter (shown in Fig.1) and a dynamic leakage test system (shown in Fig.2) were used to measure static leakage rate (Qs) and dynamic leakage, respectively. Results Fig.4shows the flow rate fluctuation of three models CPC in dynamic leakagetest due to the pressure variation inside the simulated respirator cavity. The CPC 3010 is the best for the dynamic test system. Fig.5 demonstrates the process of pad calculation. Comparisons between static and dynamic leakage are shown in Fig.8 and Fig.9. The results indicate the good correlation between static and dynamic leakage. A valve with 340 mL/min is to demonstrate the cover protective effect in dynamic leakage, and the installation of a valve cover and/or a foam piece help increase the protective effect. i.e., reduction of the pad as shown in Fig.10 The effect of sampling probe location on pad is shown in Fig.6, and finally 5.5 cm between valve and sampling probe is used. The dynamic leakage of four valves testedis shown in Fig.7. The same leakage trend both in static and dynamic leakage test. Conclusions and Recommendations The dynamic leakage correlates well to the static leakage. The static leakage test method is handy and fast; nevertheless, the dynamic leakage test method is the only way to study aerosol loading effect and develop a new high protection exhalation valve.