Raw material supply device

A raw material supply device for supplying a glass-forming raw material gas in the form of a mixed gas consisting of said glass-forming raw material gas and a carrier gas to a vapor deposition device for producing a preform of an optical fiber, the supply device comprising:

• a pressurized main raw material container having means for supplying said glass-forming gas as said mixed gas from said main raw material container to said vapor deposition device for producing a preform, a secondary raw material container having a pressurizable interior and means to pressurize said interior, said secondary container being provided adjacent to said pressurized main raw material container, means for providing liquid glass-forming raw material to said secondary raw material container, pipe means for conveying raw material liquid phase portions from said secondary container to said main container, said pipe means connected to both of said containers at their respective bottoms or substantially at said bottoms, said pipe means comprising a first pipe including a switching valve at a mid portion of said pipe, means for opening and closing said switching valve in response to fluid level in said main container, and means for adjusting the flow rate of the raw material liquid into said main container, such that the flow into the main container is controlled relative to the flow of raw material out of the main container.