The Railway Technical Research Institute has developed a drier composed of a new material, a hollow fiber, for railway rolling stock air brake. The new drier makes use low fibers are made of fluorine-based polymer membrane and withstand long use without requiring replacement. As this system features simple construction, small size and lightweight, it is best suited for railway rolling stock. It dehumidifies compressed air by passing it in the hollow fiber membrane. Vapor pressure difference between inside and outside of the membrane causes the vapor in the compressed air to be osmosed and discharged from the membrane external walls together with purged air.
The hollow fiber drier features:
(1) Longterm maintenance free characteristics
(2) Simple construction without requiring power supply
(3) Low cost (about 1/2 of ordinary drier)
(4) Compact and lightweight
(5) Easy installation
The system has a processing capacity of about 2000 L/min, and it used for compressors mounted on railway vehicles. It prevents defective operations of braking systems and door opening-closing systems, and displays and anti-freeze effect in winter. This system is of low cost and main-tenance free, so it will take the place of ordinary driers composed of absorbent.

Dehumidification interaction of hollow fiber membrane	Construction of dehumidifying module
Flow rate and dew point of dehumidifying module	Hollow fiber drier for railway rolling stock air brake