Patent ID: 8104513

Claim:
A gas flow path switching unit for setting a gas flow path to allow a target gas introduced from a gas inlet to be discharged from one of a number n of gas outlets, wherein n is an integer equal to or greater than 3, according to control of a supply of a switching gas, said gas flow path switching unit comprising: a) a target gas passage for allowing said target gas to pass therethrough, said target gas passage including a main passage having a proximal end serving as said gas inlet, and a number n of branch passages each provided with a respective one of said gas outlets at a terminal end thereof, said branch passages being formed by branching said main passage into two sub passages at a branch point defined by a distal end of said main passage and further branching at least one of said sub passages into two sub-sub passages at a branch point defined by a distal end of said sub passage; and b) at least a number n of switching-gas supply passages connected to respective intermediate positions of said n branch passages to supply said switching gas thereto; wherein the number of said at least n switching-gas supply passages connected to respective intermediate positions of said n branch passages is n, wherein said gas flow path switching unit further comprises switching-gas supply control means operable to supply said switching gas to each of said n switching-gas supply passages in such a manner that a gas supply pressure in a specific one of a number n of switching-gas supply ports of said n switching-gas supply passages becomes less than that in the remaining switching-gas supply ports, whereby said target gas is discharged from the gas outlet at the terminal end of one of said branch passages which is supplied with said switching gas from said specific switching-gas supply port at the gas supply pressure less than that in said remaining switching-gas supply ports; where said switching-gas supply control means includes: at least a number n−1 of valves each operable to allow said switching gas supplied from a switching-gas entrance thereof to be selectively discharged from one of two switching-gas exits thereof; and at least a number n−1 of resistance tubes each connecting between said two switching-gas exits of a corresponding one of said valves.