Apparatus and process for supplying gas

A process for supplying gas from a gas supplying apparatus to an analyzing instrument, said apparatus including a main switching valve in the form of a 4-way block valve having two inflow ports and two outflow ports, a connection passage connected to the analyzing instrument to which a first of the two outflow ports is connected, an exhaust passage having a flow rate regulator to which a second of the two outflow ports is connected, a pair of common gas supplying passages respectively connected to the two inflow ports of the 4-way block valve, one of first or second switching valves connected to each of the pair of common gas supplying passages respectively, first and second gas supplying passages connected to the first switching valve, and third and fourth gas supplying passages connected to the second switching valve, said process comprising:

• connecting said first switching valve at said first gas supplying passage to a first source of a first reactive gas and at said second gas supplying passage to a second source of a first non-reactive gas, and connecting said second switching valve at said third gas supplying passage to a third source of a second reactive gas and at said fourth gas supplying passage to a fourth source of a second non-reactive gas;
• supplying the second non-reactive gas from the second switching valve to the main switching valve, in the case of supplying the first reactive gas to the instrument from the first switching valve via the main switching valve;
• switching the first switching valve supplying the first reactive gas in order to supply the first non-reactive gas, in the case of switching the first reactive gas to be supplied to the instrument to the second reactive gas coming from the second switching valve;
• and
• switching the main switching valve such that the first reactive gas to be supplied to the instrument is switched to the second reactive gas coming from the second switching valve after the concentration of the first reactive gas from the first switching valve is lowered below a predetermined concentration.