The instant invention is an apparatus for maintaining approximately constant tension of a curtain (22) between a drive roller (70) and a storage roller (40). The constant tension is achieved by pre-tensioning the curtain (22) between the drive roller (70) and the storage roller (40) and then maintaining approximately the same amount of tension by rotating the reference to which one end of a spring (52) is attached. The rotating reference is a shaft (45) which is affixed to and rotates with a shaft gear (50). The other end of the spring (52) is affixed to a cylindrical tube member, i.e., the storage roller (40), upon which the flexible curtain (22) is stored. A motor driven gear (77) drives a gear affixed to the drive roller (70). The gear (66) affixed to the drive roller (70) in turn drives idler gears (58, 62) which in turn drive the shaft gear (50). A method of using the apparatus is also disclosed.