In the standard version, the materials in touch with gases are fluorinated plastics, highly corrosion resistant. The effects of some characteristics of these materials (in particular the permeability) make them unsuitable for some specific application:
- measurement of oxygen in ppm. In this case, in spite of the overpressure of the internal circuits with respect to the environment, some of the oxygen contained in air permeates through the tubes polluting the sample.
- some components, such as HF, HCl and HN3 have the characteristic of saturate the surface porosity of the plastics. The adsorption process takes long time and, particularly when concentration is low, the selective subtraction of molecules causes an important concentration reduction that return regular only when plastics are saturated (up to a couple of hours time).
We then made available execution 'All steel' for internal modules, which are connected together and to the interface panel with stainless steel 1/8' tubes and compression fittings. All these components are made by AISI 316L , pickled and electropolished. Made by plastic material (PEEK) remains only the body of the solenoid valves, while all the seals are fluorinated elastomers. To achieve significant reductions in response times it is necessary that also the connections towards the external cylinder of 'Span' and to the analyzer are steel made . The counterpart over the use of plastics is a moderate increase in the cost (10%) and weight (25%) and the lower flexybility of the external connections.