Gas supply piping system and method for replacing purifier

A gas supply piping system, suitable for transporting a gas from a gas supply terminal to a machine terminal, comprising:

• a main supply pipe, connected to the gas supply terminal;
• a first branch supply pipe and a second branch supply pipe, connected to the main supply pipe and the machine terminal respectively;
• a first purifier and a second purifier, connected to the first and second branch supply pipes respectively;
• a first valve and a second valve, connected to the first and second branch supply pipes respectively, wherein the first valve is located between the first purifier and the gas supply terminal, and the second valve is located between the second purifier and the gas supply terminal;
• a first backup pipe, connecting the first branch supply pipe to the second branch supply pipe;
• a third valve, connected to the first backup pipe;
• and
• a fourth valve and a fifth valve, connected to the first and second branch supply pipes respectively, wherein the fourth valve is located between the first purifier and the first backup pipe, and the fifth valve is located between the second purifier and the first backup pipe.