an apparatus for coating surfaces consists of a basin , open to the atmosphere , divided into two channels by a wall running perpendicular to the coating direction . liquid is supplied to the primary channel , the channel farther from the curtain . a continuous , adjustable gap between the dividing wall and the bottom of the basin offers resistance to flow but passes the coating composition from the primary to the secondary channel . the secondary channel has an edge that is horizontal and relatively low so that the coating composition overflows it to form a free - falling curtain . the dividing wall , by providing flow resistance , assists in distributing the supplied coating composition along the length of the primary channel , and reduces any flow disturbances caused by the entering coating composition . the secondary channel promotes additional evening of the flow distribution before the curtain forms .