RR635 - Effect of tubing type on gas detector sampling systems
Objectives
This investigation was designed to determine the effect of polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) and Tygon tubing on the response times of the detection systems utilised to monitor Hydrogen Sulphide (H2S), Nitrogen Dioxide (NO2), Nitric Oxide (NO) and Toluene (C7H8).
Main Findings
- With the exception of C7H8 passing through Tygon tubing, the change in T90 as a function of tubing length is comparable within accuracy limits for all gases at each corresponding tubing type and diameter.
- The times taken for H2S and NO to reach T90, T100 and T10 are comparable for all corresponding dimensions of PTFE and FEP tubing, but while the time taken to reach T10 is comparable for Tygon tubing, the times taken to reach T90 and T100 are considerably longer for all corresponding dimensions.
- The times taken for NO2 to reach T90 and T10 are comparable for all corresponding dimensions of PTFE, FEP and Tygon tubing and to reach T100 for all but the largest dimension of Tygon tubing.
- The times taken for C7H8 to reach T90 and T100 through all dimensions of Tygon tubing were greater than one hour.
- The times taken for C7H8 to reach T90 and T10 are comparable for all corresponding diameters of the 2.5 m and 5 m lengths of PTFE and FEP tubing, but the times taken to reach T90 in the 10 m lengths of PTFE and FEP tubing are noticeably longer and to reach T100 are considerably longer for PTFE tubing than for FEP tubing.
- The times taken for H2S, NO and NO2 to reach each level of concentration are reasonably comparable for all corresponding dimensions of PTFE and FEP tubing, but are noticeably longer for all corresponding dimensions of Tygon tubing.
- The times taken for NO2 to reach each level of concentration are generally noticeably shorter than the times taken by H2S, NO and C7H8 for all corresponding dimensions of PTFE, FEP and Tygon tubing.
- The times taken for C7H8 to reach each level of concentration are considerably longer than the times taken by H2S, NO and NO2 for all corresponding dimensions of PTFE and FEP tubing.
Recommendations
PTFE and FEP can be used with minimal effect when sampling H2S, NO and NO2. Tygon may be used when sampling H2S, NO and NO2 if PTFE and FEP are not available providing the delay time is not an issue, but the tube dimensions must be as small as practically possible without restricting the flow rate of the sampling instrument. Tygon is not suitable for use in sampling C7H8 but PTFE and FEP may be used providing the delay time is not an issue.
Assistance in the use of Adobe Acrobat PDF files is available on our FAQs page.