1、International Standard INTERNATIONAL ORGANIZATION FOR STANDARDIZATION*MEYHAPOfiHAR OPAHH3Al connecting tubing; particulate filter and filter holder; absorber; protection filter; sampling pump; gas meter or air-flow regulator. A schematic layout of a typical assembly system is shown in The internal d
2、iameter of the tubing shall be 6 to 8 mm and the figure 1 : internal surface shall be smooth. 5.1 Air intake No particular design of air intake is required for this Inter- national Standard concerning determination of gaseous sulphur compounds only. If the air intake may be exposed to precipitation,
3、 an inverted funnel may be used as protection, as shown in figure 2. If it is intended to carry out other determinations, e.g. concen- tration of black smoke with the same equipment (see clause 21, the air must be drawn in through an air intake of appropriate diameter. 5.2 Connecting tubing 5.2.1 Di
4、mensions Air intake Particulate Absorber Protection filter and filter filter holder Figure 1 - Block diagram of sampling equipment Sampling pump Gas meter or air-flow regulator - Protecting funnel Figure 2 - Air intake with protecting funnel IS0 4219-1979 (E) 5.2.2 Material In addition to the genera
5、l requirements for materials, plastics materials used shall be protected from actinic activity and preferably should be covered with a material having a low ther- mal conductivity. All tubing shall be airtight. Regular cleaning of the tubing is recommended. The following materials, in order of prefe
6、rence according to descending effectiveness, may be used : a) Polytetrafluorethylene (PTFE). Although chemically inert, PTFE is not flexible and difficulty may be experienced in making connections. Connections with PTFE can be made successfully using connectors which are available in PTFE. In additi
7、on, in view of the inflexibility of PTFE, there is no need to use PTFE downstream of the sample absorber. Rubber vacuum hose should be the preferred material since it is flexible, makes good seals and will not affect the sample because the components of interest have already been removed. b) Glass.
8、Glass is fragile. It is suggested that connections to components be made using butt joints with flexible PVC tubing. c) Polypropylene (polyethylene). Agents used for cleaning tubing shall 5.3 Particulate filter be sulphur free. The assembly shall be airtight in use; hence, an appropriate clamping de
9、vice shall be used together with an annular seal. Air shall be drawn upwards through the filter. 5.3.1 Filter material The material of the filter shall be chemically inert with respect to sulphur compounds, and shall not be hygroscopic. The filter shall possess high efficiency (99 %I for particles a
10、bove 0,3 pm. If the filter is being used simply to remove particulate matter (which interferes with some methods of analysis), a suitable filter is a pad of polystyrene fibrest). This filter has excellent efficiency and low pressure drop, and the material is inert. Other kinds of inert filter can al
11、so be used. The use of glass fibre filter material is not recommended as it is too reactive (see first paragraph). NOTE - Under conditions of high humidity, the particulate filter may become damp and thus absorb some sulphur compounds from the air passing through it. These conditions should be noted
12、 in the test report. The heating of the filter under such conditions is not recommended due to the possibility of side reactions. However, under some climatic conditions, it is found necessary to warm the filter above the dew point. 5.3.2 Filter holder The filter holder shall be made from inert mate
13、rial, for an exam- ple an inert form of PVC, 5.4 Absorber The design of the absorption bottle, in which the absorption solution is contained, is dependent on the particular analysis to be employed and on the sampling flow rate. The relevant Inter- national Standards shall be consulted. 5.5 Protectio
14、n filter If a liquid absorbent is employed, it may be necessary to insert a trap between the absorption bottle and the gas meter (or the air-flow regulator) to protect the latter from absorbing solution droplets and/or harmful gases. The design of the trap is not critical, provided that air is not a
15、llowed to enter the system through leakage (it will normally be under slight suction). 5.6 Gas meter or air-flow regulator In order to calculate the relevant concentration, the volume of air sampled must be known. The volume is best measured by an integrating method, for example by using a dry-gas m
16、eter. This shall be able to record the volume of sampled air to a suff i- cient accuracy at the flow rate used. A flow-regulat.ing system based on the use of a critical orifice may alternatively be used. The flow sha!l then be checked at the beginning and end of the sampling period at the air intake
17、 with a device such as a variable-area flow meter to ensure that the flow rate has not changed because of partial plugging of the orifice. Calibration of these meters or orifices may be carried out by comparison with a laboratory wet-gas meter which has itself been subjected to primary calibration w
18、ithin the preceding 2 years. 5.7 Sampling pump The most suitable device for sampling is a constant-flow air pump. The type of pump should preferably be chosen for the intended air flow rate as it is not good practice to control a pump flow rate by voltage variations. Unless the pump is placed after
19、the gas meter, it shall be leak proof. 6 Installation Install the equipment in an environment in which it is not ex- posed to extreme temperatures or to direct sunlight for long periods. Arrange the air intake (5.1) so that it is at least 1 m from all obstacles, including sampling equipment, and mor
20、e than 3 m 1 I For example, Microsorban. IS0 4219-1979 (E) above the nearest large area of horizontal surface. The tubing or funnel shall point vertically downwards. Take care to avoid placing the air intake anywhere near local sources of pollution, such as a low-level chimney or an exhaust vent. NO
21、TE - The choice of a site which is representative of the relevant concentration In a given geographical area, and the number of sites re- quired for adequate coverage of a given area, will be the subject of other International Standards, Arrange the connecting tubing (5.21 in such a way that there a
22、re no loops in which water may collect and no radii less than 50 mm. The latter condition is particularly important if a black smoke index is being determined with the same equipment. The total length of tubing between air intake and absorber (5.4) shall be as short as possible and in any case shall be less than 6 m. Check that all connections between the components of the equipment are airtight.
